Co-reporter:Nicole Lenca, Colin F. Poole
Journal of Chromatography A 2017 Volume 1525(Volume 1525) pp:
Publication Date(Web):24 November 2017
DOI:10.1016/j.chroma.2017.10.015
•System map for SLB-IL60 for the temperature range from 80 to 280 °C.•Intermolecular interactions responsible for retention are characterized.•The SLB-IL60 column is a moderate hydrogen-bond acid at temperatures <280 °C.•The SLB-IL60 column has complementary separation properties to SLB-IL100.The solvation parameter model is used to prepare a system map for the retention of volatile organic compounds on the ionic liquid stationary phase 1,12-di(tripropylphosphonium)dodecane bis(trifluoromethylsulfonyl)imide (SLB-IL60) by gas chromatography over the temperature range 80–280 °C. Retention is governed by dispersion, dipole-type and hydrogen-bonding interactions with a different temperature dependence. The hydrogen-bond acidity of the SLB-IL60 column is unexpected since the stationary phase contains no hydrogen-bond acid groups and is not obviously connected to contributions from the deactivated column wall. The polarity number is shown to be a poor indicator of column retention properties. Principal component analysis with the system constants of the solvation parameter model as variables indicates that the properties of SLB-IL60 are not duplicated by any of the common poly(siloxane) and poly(ethylene glycol) stationary phase chemistries in common use for column preparation. The SLB-IL60 column has similar selectivity to a poly(cyanopropylphenyldimethylsiloxane) stationary phase containing 50% cyanopropylphenyl siloxane monomer but the two columns are not selectivity equivalent. Poly(ethylene glycol) stationary phases indicated as most similar to SLB-IL60 based on their polarity numbers are shown to have quite different selectivity.
Co-reporter:Sanka N. Atapattu;Mike B. Praseuth
Chromatographia 2017 Volume 80( Issue 9) pp:1279-1286
Publication Date(Web):12 July 2017
DOI:10.1007/s10337-017-3350-y
The system constants of the solvation parameter model are used to prepare system maps for the retention of small neutral compounds on an ethyl-bridged, ocatadecylsiloxane-bonded superficially porous silica stationary phase (Kinetex EVO C18) for aqueous mobile phases containing 10–70% (v/v) methanol or acetonitrile. Electrostatic interactions (cation-exchange) are important for the retention of weak bases with acetonitrile–water but not methanol–water mobile phase compositions. Compared with a superficially porous octadecylsiloxane-bonded silica stationary phase (Kinetex C18) with a similar morphology but different topology statistically significant differences in selectivity at the 95% confidence level are observed for neutral compounds that vary by size and hydrogen-bond basicity with other intermolecular interactions roughly similar. These selectivity differences are dampened with acetonitrile–water mobile phases, but are significant for methanol–water mobile phase compositions containing <30% (v/v) methanol. A comparison of a totally porous ethyl-bridged, octadecylsiloxane-bonded silica stationary phase (XBridge C18) with Kinetex EVO C18 indicated that they are effectively selectivity equivalent.
Co-reporter:Nicole Lenca, Sanka N. Atapattu, Colin F. Poole
Journal of Chromatography A 2017 Volume 1526(Volume 1526) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.chroma.2017.10.037
•Descriptors for 94 hydrogen-bonding compounds.•Discussion of the relationship between structure and hydrogen-bonding properties.•Compounds are suitable as calibration compounds for characterizing separation systems.•Compounds can be merged into a larger database of compounds and their descriptors.Retention factors obtained by gas chromatography and reversed-phase liquid chromatography on varied columns and partition constants in different liquid-liquid partition systems are used to estimate WSU descriptor values for 36 anilines and N-heterocyclic compounds, 13 amides and related compounds, and 45 phenols and alcohols. These compounds are suitable for use as calibration compounds to characterize separation systems covering the descriptor space E = 0.2–3, S = 0.4–2.1, A = 0–1.5, B = 0.1–1.5, L = 2.5–10.0 and V = 0.5–2.2. Hydrogen-bonding properties are discussed in terms of structure, the possibility of induction effects, intramolecular hydrogen bonding and steric factors for anilines, amides, phenols and alcohols. The relationship between these parameters and observed descriptor values are difficult to predict from structure but facilitate improving the general occupancy of the descriptor space by creating incremental changes in hydrogen-bonding properties. It is verified that the compounds included in this study can be merged with an existing database of compounds recommended for characterizing separation systems.
Co-reporter:Nicole Lenca, Colin F. Poole
Journal of Chromatography A 2017 Volume 1524(Volume 1524) pp:
Publication Date(Web):17 November 2017
DOI:10.1016/j.chroma.2017.09.064
•System map for SLB-IL76 for the temperature range from 80 to 240 °C.•Intermolecular interactions responsible for retention are characterized.•Hydrogen-bond acidity is not clearly connected with the amide groups of the cation.•The SLB-IL76 column has complementary separation properties to HP-88 and similar bis(cyanopropyl)siloxane stationary phases.The solvation parameter model is used to construct a system map for the retention of volatile organic compounds on the ionic liquid stationary phase tri(tripropypphosphoniumhexanamido)triethylamine bis(trifluoromethylsulfonyl)imide (SLB-IL76) over the temperature range 80–240 °C. The SLB-IL76 stationary phase is moderately cohesive and strongly dipolar/polarizable and hydrogen-bond basic but only a weak hydrogen-bond acid. Electron lone pair interactions are weak and make only a minor contribution to the retention mechanism. The separation properties of SLB-IL76 highlight the difficulty of designing new stationary phases from ion structures as the presence of amide groups in the cation don’t seem to contribute significantly to the hydrogen-bond acidity of SLB-IL76. The separation properties of SLB-IL76 are closest to the bis(polycyanopropyl)siloxane stationary phases with a high percentage of bis(cyanopropyl)siloxane monomer and could be used in method development when a stationary phase with similar gross retention characteristics but different selectivity is required.
Co-reporter:Colin F. Poole
Journal of Chromatography A 2017 Volume 1527(Volume 1527) pp:
Publication Date(Web):8 December 2017
DOI:10.1016/j.chroma.2017.10.061
•Partition constants for over 300 compounds of industrial, environmental and biological interest.•Nineteen totally organic biphasic systems.•Selection guide for biphasic systems.•System constants facilitate the estimation of further partition constants.A database of partition constants for more than 300 compounds of industrial, environmental and biological interest in nineteen totally organic biphasic systems is reported. The biphasic systems consist of the polar organic solvents acetonitrile, methanol, N,N-dimethylformamide, dimethyl sulfoxide, formamide, propylene carbonate, ethylene glycol, ethanolamine and 3,3,3-trifluoroethanol with n-heptane or n-hexane (10 systems), isopentyl ether (5 systems), 1,2-dichloroethane (2 systems) and 1-octanol (2 systems) of suitable low mutual solubility. The solvation parameter model is used to identify compounds with extreme partition constant values and to develop a selection guide based on the cluster analysis of the model system constants to identify biphasic systems for liquid–liquid extraction.
Co-reporter:Colin F. Poole, Nicole Lenca
Journal of Chromatography A 2017 Volume 1486(Volume 1486) pp:
Publication Date(Web):24 February 2017
DOI:10.1016/j.chroma.2016.05.099
•Critical summary of the literature from 2005 to 2016.•Interphase model used to interpret retention mechanism.•Methods to identify surrogate chromatographic models for biopartitioning provided.•Anomalies in system maps explained.The solvation parameter model is widely used to provide insight into the retention mechanism in reversed-phase liquid chromatography, for column characterization, and in the development of surrogate chromatographic models for biopartitioning processes. The properties of the separation system are described by five system constants representing all possible intermolecular interactions for neutral molecules. The general model can be extended to include ions and enantiomers by adding new descriptors to encode the specific properties of these compounds. System maps provide a comprehensive overview of the separation system as a function of mobile phase composition and/or temperature for method development. The solvation parameter model has been applied to gradient elution separations but here theory and practice suggest a cautious approach since the interpretation of system and compound properties derived from its use are approximate. A growing application of the solvation parameter model in reversed-phase liquid chromatography is the screening of surrogate chromatographic systems for estimating biopartitioning properties. Throughout the discussion of the above topics success as well as known and likely deficiencies of the solvation parameter model are described with an emphasis on the role of the heterogeneous properties of the interphase region on the interpretation and understanding of the general retention mechanism in reversed-phase liquid chromatography for porous chemically bonded sorbents.
Co-reporter:Sanka N. Atapattu, Colin F. Poole, Mike B. Praseuth
Journal of Chromatography A 2016 Volume 1468() pp:250-256
Publication Date(Web):14 October 2016
DOI:10.1016/j.chroma.2016.09.045
•System maps for a Kenetex C-18 column provided for acetonitrile- and methanol-water mobile phases.•Intermolecular interactions responsible for retention are characterized.•Retention properties are typical of octadecylsiloxane-bonded silica stationary phases.The system constants of the solvation parameter model are used to prepare system maps for the retention of small neutral molecules on the ocadecylsiloxane-bonded silica superficially porous particle stationary phase (Kinetex C18) for aqueous-organic solvent mobile phases containing 10–70% (v/v) methanol or acetonitrile. A comparison of the system constants with eight commercially available octadecylsiloxane-bonded silica columns for the same separation conditions confirms that the general retention properties of Kinetex C-18 are similar to totally porous octadecylsiloxane-bonded silica stationary phases and that method transfer should be no more difficult than that usually observed when substituting one octadecylsiloxane-bonded silica column for another.
Co-reporter:Colin F. Poole
Chromatographia 2016 Volume 79( Issue 5-6) pp:365-366
Publication Date(Web):2016 March
DOI:10.1007/s10337-015-2997-5
Co-reporter:Colin F. Poole
Chromatographia 2016 Volume 79( Issue 9-10) pp:647-648
Publication Date(Web):2016 May
DOI:10.1007/s10337-016-3035-y
Co-reporter:Pierre Bernard-Savary, Colin F. Poole
Journal of Chromatography A 2015 Volume 1421() pp:184-202
Publication Date(Web):20 November 2015
DOI:10.1016/j.chroma.2015.08.002
•Overview of instrumentation for high-performance thin-layer chromatography.•Semi- and full-automation of the separation process.•Techniques for in situ identification and quantification.•Current state-of-the-art in instrumental thin-layer chromatography.High performance column and thin-layer chromatography are both instrumental techniques but differ in that column chromatography requires a fully integrated instrument platform with high pressure capability while for thin-layer chromatography separate devices are used for each unit operation, usually at or close to atmospheric pressure, and afford higher flexibility supporting on-line or off-line operation. The unit operations of thin-layer chromatography are defined as sample application, development and evaluation with derivatization as an optional step. The diversity of equipment for each operation contributes to the flexibility of analysis by thin-layer chromatography and supports manual, semi-automated or full-automation of the separation process. Instrument platforms are more than a convenience as they affect performance, repeatability, sample detectability, and time management. The current trend in thin-layer chromatography is to make the unit operations independent of the user so that analysts can perform other tasks while each step is performed. In addition, in thin-layer chromatography it is general practice to separate several samples simultaneously, and instrument platforms are required to accommodate this feature. In this article, we review contemporary instrumentation employed in thin-layer chromatography for sample application, development, derivatization, photodocumentation, densitometric evaluation, and hyphenation with spectroscopic detectors with an emphasis on the variety and performance of commercially available systems. Some suggestions for best practices and avoidance of common mistakes are included.
Co-reporter:Nicole Lenca
Chromatographia 2015 Volume 78( Issue 1-2) pp:81-88
Publication Date(Web):2015 January
DOI:10.1007/s10337-014-2790-x
The solvation parameter model is used to characterize the retention properties of the ionic liquid stationary phase 1,9-di(3-vinylimidazolium)nonane bis(trifluoromethylsulfonyl)imide (SLB-IL100) over the temperature range 60–200 °C. The results are presented in the form of a system map comprising a continuous plot of the system constants of the solvation parameter model determined at 20 °C intervals as a function of column temperature. The ionic liquid stationary phase is a cohesive, polar solvent with significant hydrogen-bonding capability. It differs from polar siloxane-based and poly(ethylene glycol) stationary phases by being a moderate hydrogen-bond acid and is shown to possess separation properties that are not duplicated in a comprehensive database of system constants for commercially available open-tubular columns.
Co-reporter:Colin F. Poole
Chromatographia 2015 Volume 78( Issue 9-10) pp:737-738
Publication Date(Web):2015 May
DOI:10.1007/s10337-015-2888-9
Co-reporter:Colin F. Poole, Nicole Lenca
TrAC Trends in Analytical Chemistry 2015 Volume 71() pp:144-156
Publication Date(Web):September 2015
DOI:10.1016/j.trac.2014.08.018
•Solvent classification reported for ionic liquids.•Physicochemical properties of ionic liquids used for sample preparation.•The use of ionic liquids in microextraction techniques.•The green credentials of ionic liquids for use in sample preparation.Room-temperature ionic liquids (RTILs) are novel solvents composed entirely of ions. They can dissolve a wide range of compounds, while some possess virtually no vapor pressure over a wide temperature range, and have high thermal stability, low toxicity, and low flammability, properties desirable of green solvents. Applications that take advantage for their characteristic properties are starting to appear regularly embodied in techniques, such as liquid-phase microextraction, solid-phase microextraction, and microwave-assisted extraction. In this review, we present a contemporary picture of how, where and when to use ILs in sample-preparation techniques, while recognizing limitations that inhibit their use for some applications. Since the number of potential RTILs is very large, and only a small number have been evaluated in laboratory studies, it is important not to overgeneralize on their potential as general solvents based on this small database of rather limited chemical diversity.
Co-reporter:Colin F. Poole
Chromatographia 2015 Volume 78( Issue 15-16) pp:1103-1104
Publication Date(Web):2015 August
DOI:10.1007/s10337-015-2902-2
Co-reporter:Colin F. Poole
Chromatographia 2015 Volume 78( Issue 11-12) pp:839-840
Publication Date(Web):2015 June
DOI:10.1007/s10337-015-2880-4
Co-reporter:Colin F. Poole
Chromatographia 2015 Volume 78( Issue 21-22) pp:1415-1416
Publication Date(Web):2015 November
DOI:10.1007/s10337-015-2945-4
Co-reporter:Colin F. Poole, Nicole Lenca
Journal of Chromatography A 2014 Volume 1357() pp:87-109
Publication Date(Web):29 August 2014
DOI:10.1016/j.chroma.2014.03.029
•Critical review of ionic liquids as stationary phases for gas chromatography.•Discussion of methods to evaluate column quality.•Discussion of methods to characterize stationary phase selectivity.•Overview of applications using commercially available ionic liquid columns.Ionic liquids have moved from novel to practical stationary phases for gas chromatography with an increasing portfolio of applications. Ionic liquids complement conventional stationary phases because of a combination of thermophysical and solvation properties that only exist for ionic solvents. Their high thermal stability and low vapor pressure makes them suitable as polar stationary phases for separations requiring high temperatures. Ionic liquids are good solvents and can be used to expand the chemical space for separations. They are the only stationary phases with significant hydrogen-bond acidity in common use; they extend the hydrogen-bond basicity of conventional stationary phases; they are as dipolar/polarizable as the most polar conventional stationary phases; and some ionic liquids are significantly less cohesive than conventional polar stationary phases. Problems in column coating techniques and related low column performance, column activity, and stationary phase reactivity require further exploration as the reasons for these features are poorly understood at present.
Co-reporter:Thiloka C. Ariyasena, Colin F. Poole
Journal of Chromatography A 2014 Volume 1361() pp:240-254
Publication Date(Web):26 September 2014
DOI:10.1016/j.chroma.2014.08.008
•Validation of descriptor quality.•Atom fragment model for estimating descriptors.•Prediction of water-based system properties.•Nonaqueous systems to determine descriptors.Retention factors on several columns and at various temperatures using gas chromatography and from reversed-phase liquid chromatography on a SunFire C18 column with various mobile phase compositions containing acetonitrile, methanol and tetrahydrofuran as strength adjusting solvents are combined with liquid–liquid partition coefficients in totally organic biphasic systems to calculate descriptors for 23 polycyclic aromatic hydrocarbons and eighteen related compounds of environmental interest. The use of a consistent protocol for the above measurements provides descriptors that are more self consistent for the estimation of physicochemical properties (octanol–water, air–octanol, air–water, aqueous solubility, and subcooled liquid vapor pressure). The descriptor in this report tend to have smaller values for the L and E descriptors and random differences in the B and S descriptors compared with literature sources. A simple atom fragment constant model is proposed for the estimation of descriptors from structure for polycyclic aromatic hydrocarbons. The new descriptors show no bias in the prediction of the air–water partition coefficient for polycyclic aromatic hydrocarbons unlike the literature values.
Co-reporter:Colin F. Poole, Thiloka C. Ariyasena, Nicole Lenca
Journal of Chromatography A 2013 Volume 1317() pp:85-104
Publication Date(Web):22 November 2013
DOI:10.1016/j.chroma.2013.05.045
•Identification of surrogate chromatographic models for estimating environmental properties.•Use of chromatographic measurements for calculating descriptors.•Characterization of environmental processes using the solvation parameter model.•Estimating environmental properties using correlation models.This article provides an overview of chromatographic methods as surrogate models for environmental processes and for the determination of descriptors for compounds of environmental interest. The solvation parameter model is the link to the identification of suitable chromatographic models for the estimation of environmental properties using a set of tools that allow screening of chromatographic databases for the selection of candidate systems. As an alternative approach, many transport and distribution properties of environmental interest can be described directly by the solvation parameter model. Environmental properties for compounds with known descriptors can then be predicted through these models. The central role chromatographic methods, together with liquid–liquid partition coefficients, occupy in the determination of the six descriptors used in the solvation parameter model is detailed. There is a current need to accelerate efforts to expand the coverage of environmental process models by incorporating more complex molecules of contemporary environmental interest. For many of these molecules descriptor values are unavailable and their determination should be prioritized.
Co-reporter:Colin F. Poole
Journal of Chromatography A 2013 Volume 1296() pp:2-14
Publication Date(Web):28 June 2013
DOI:10.1016/j.chroma.2013.01.097
Alkylsilyl reagents are the most widely used reagents for the derivatization of polar compounds containing labile hydrogen atoms for gas chromatography. In this article the reagents and reaction conditions for the formation of trimethylsilyl, alkyldimethylsilyl (particularly t-butyldimethylsilyl), cyclic siliconides, haloalkyldimethylsilyl, and flophemesyl (pentafluorophenyldimethylsilyl) derivatives for a wide range of functional groups are reviewed. The importance of steric hindrance on reaction rates and completion, choice of reaction conditions, stability of derivatives, and options for selective detection are described.Highlights► Critical discussion of reaction conditions for formation of alkyldimethylsilyl ethers. ► Overview of methods for the selective detection of alkyldimethylsilyl ethers. ► Includes up to date information on the stability of alkyldimethylsilyl ethers.
Co-reporter:Colin F. Poole
Journal of Chromatography A 2013 Volume 1296() pp:15-24
Publication Date(Web):28 June 2013
DOI:10.1016/j.chroma.2013.01.108
The electron-capture detector is a structure-selective detector with a wide response range for organic compounds. It is predominantly used to determine halogen-containing compounds, nitroaromatic compounds, and compounds with conjugated systems connecting at least two weak electrophore groups. High sensitivity and selectivity make it a general choice for trace analysis. For compounds with reactive functional groups and weak electron capture properties, derivatization affords a facile method to facilitate their detection. Reagents and reaction conditions for the formation of derivatives with electron-capturing properties are described in this review. The common methods for introducing an electrophore into organic compounds with polar functional groups include silylation, acylation, alkylation, esterification, Schiff base reagents, addition of halogens, and cyclic derivatives formed with bifunctional compounds. These reactions include reagents for general use as well as functional group selective reagents. In addition to the selection of reagents, the effect of the detector operating parameters on its response and details of the electron-capture mechanism for common derivatives are discussed.Highlights► Overview of reagents and conditions for the formation of derivatives for use with the electron-capture detector. ► Overview of the factors that determine the response of the electron-capture detector to different compounds. ► Effect of the detector temperature on the response of the electron-capture detector.
Co-reporter:Colin F. Poole;Thushara Karunasekara ;Thiloka C. Ariyasena
Journal of Separation Science 2013 Volume 36( Issue 1) pp:96-109
Publication Date(Web):
DOI:10.1002/jssc.201200709
Partition between two immiscible solvents is widely used in sample preparation procedures for matrix simplification and isolation of target analytes, for separations using countercurrent, centrifugal partition, and liquid–liquid chromatography, and as a method for determining descriptors for use in modeling chemical, biological, and environmental processes. Until recently, most applications employed water as one component of the biphasic system. For compounds of low water solubility or stability, a series of totally organic biphasic systems have been developed to enhance the application range of liquid–liquid partition methods. These systems, their characterization using the solvation parameter model, and applications to sample preparation and the determination of descriptors are described in this review.
Co-reporter:Thiloka C. Ariyasena
Chromatographia 2013 Volume 76( Issue 3-4) pp:157-164
Publication Date(Web):2013 February
DOI:10.1007/s10337-013-2387-9
Partition coefficients for varied compounds were determined for the ethanolamine–organic solvent biphasic partition systems where the organic solvent is n-heptane or isopentyl ether. These partition coefficient databases are analyzed using the solvation parameter model facilitating a quantitative comparison of the ethanolamine-based partition system with other totally organic partition systems. Ethanolamine is a cohesive solvent, reasonably dipolar/polarizable, strongly hydrogen-bond basic, and moderately hydrogen-bond acidic. Ethanolamine–organic solvent systems afford a complementary approach to other totally organic biphasic partition systems for sample preparation and descriptor measurements for compounds of low water solubility. In particular, ethanolamine is a stronger hydrogen-bond base than other polar organic solvents and water and forms biphasic systems that should be well suited to measuring the hydrogen-bond acidity descriptor and for the selective extraction of hydrogen-bond acids soluble in n-heptane or isopentyl ether.
Co-reporter:Thiloka C. Ariyasena
Chromatographia 2013 Volume 76( Issue 15-16) pp:1031-1039
Publication Date(Web):2013 August
DOI:10.1007/s10337-013-2496-5
Partition coefficients for varied compounds were determined for the triethylamine–organic solvent biphasic partition systems where the organic solvent is dimethyl sulfoxide, ethanolamine or formamide. These partition coefficient databases are analyzed using the solvation parameter model facilitating a quantitative comparison of the triethylamine-based partition system with other totally organic partition systems. By comparison with the system constants for the biphasic systems formed between n-heptane and dimethyl sulfoxide, ethanolamine and formamide, triethylamine is a weakly cohesive solvent (slightly stronger than n-heptane), weakly dipolar/polarizable (only slightly larger than n-heptane), and non-hydrogen-bond acidic. Triethylamine is moderately hydrogen-bond basic, but much less so than ethanolamine, formamide and dimethyl sulfoxide, which are strong hydrogen-bond bases. The separation properties of triethylamine–dimethyl sulfoxide are more similar to the isopentyl ether-propylene carbonate biphasic system; the triethylamine-formamide system octan-1-ol-formamide biphaic system; and triethylamine–ethanolamine the 1,2-dichloroethane–formamide and 1,2-dichloroethane–ethylene glycol systems. None of these pairs of biphasic systems are selectivity equivalent. In the first case, the significant difference in cohesive properties favors the distribution of larger solutes to the triethylamine layer and the greater hydrogen-bond basicity of dimethyl sulfoxide the selective extraction of hydrogen-bond acids. For the triethylamine–formamide system larger molecules have a slight preference for transfer to the triethylamine layer compared with octan-1-ol, and hydrogen-bond bases will be selectively extracted to the formamide layer, since triethylamine is not competitive with octan-1-ol as a hydrogen-bond acid. There are few totally organic biphasic systems suitable for the determination of solute hydrogen-bond basicity (B descriptor) and the triethylamine–formamide biphasic system can be used to supplement these.
Co-reporter:Colin F. Poole
Chromatographia 2013 Volume 76( Issue 13-14) pp:867-868
Publication Date(Web):2013 July
DOI:10.1007/s10337-013-2455-1
Co-reporter:Thushara Karunasekara, Colin F. Poole
Journal of Chromatography A 2012 Volume 1235() pp:159-165
Publication Date(Web):27 April 2012
DOI:10.1016/j.chroma.2012.02.043
Retention factors on a minimum of eight stationary phases at various temperatures by gas–liquid chromatography and liquid–liquid partition coefficients for five totally organic biphasic systems were combined to estimate descriptors for 28 fragrance compounds with an emphasis on compounds that are known or potential allergens. The descriptors facilitated the estimation of several properties of biological and environmental interest (sensory irritation threshold, odor detection threshold, nasal pungency threshold, skin permeability from water, skin–water partition coefficients, octanol–water partition coefficients, absorption by air particles, adsorption by diesel soot particles, air–water partition coefficients, and adsorption by film water). The descriptors are suitable for use in the solvation parameter model and facilitate the estimation of a wide range of physicochemical, chromatographic, biological, and environmental properties using existing models.Highlights► Descriptors for 28 fragrance compounds. ► Prediction of biological and environmental properties for fragrance compounds using the solvation parameter model. ► Prediction of properties for aqueous systems based on non-aqueous chromatographic and liquid–liquid partition measurements.
Co-reporter:Thushara Karunasekara, Colin F. Poole
Journal of Chromatography A 2012 Volume 1266() pp:124-130
Publication Date(Web):30 November 2012
DOI:10.1016/j.chroma.2012.09.104
A combination of gas chromatography and liquid–liquid partitions in totally organic biphasic systems is used to determine descriptor values for compounds of low volatility suitable for characterizing open tubular columns at high temperatures. The descriptor database of varied compounds includes several difficult to determine by conventional techniques due to their low water solubility or stability. The descriptor database facilitates an expansion of the descriptor space and compound variation for characterizing separation systems. As an application the descriptor database is used to determine the system constants for SPB-Octyl, HP-5, Rxi-5Sil MS, Rtx-440, and Rtx-OPP for the temperature range 200–300 °C. As an example of the broader affect of temperature on column selectivity the variation of the system constants for Rtx-440 over the temperature range 60–300 °C is described in detail. These studies demonstrate the persistence of polar interactions to the highest temperature studied and that at high temperatures selectivity differences persist for moderately polar stationary phases.Highlights► Descriptors for compounds of low water solubility and low volatility. ► First time characterization of stationary phases at high temperatures. ► Demonstrates persistence of polar interactions at high temperatures.
Co-reporter:Colin F. Poole
Journal of Chromatography A 2012 1250() pp: 157-171
Publication Date(Web):
DOI:10.1016/j.chroma.2011.12.040
Co-reporter:Colin F. Poole
Chromatographia 2012 Volume 75( Issue 15-16) pp:949-950
Publication Date(Web):2012 August
DOI:10.1007/s10337-012-2267-8
Co-reporter:Thushara Karunasekara;Sanka N. Atapattu
Chromatographia 2012 Volume 75( Issue 19-20) pp:1135-1146
Publication Date(Web):2012 October
DOI:10.1007/s10337-012-2288-3
Retention factors on a minimum of eight stationary phases at various temperatures by gas–liquid chromatography and in acetonitrile–water and methanol–water mobile phases by reversed-phase liquid chromatography on a Synergi Polar-RP column were combined with further values taken from the literature and liquid–liquid partition coefficients for up to eight totally organic biphasic systems to estimate descriptors for 24 esters (phthalate, oleate, stearate, arbietate, adipate, succinate, sebacate, and diethylmalonate) widely used as plasticizers and solvents in industry. The descriptors facilitated the estimation of several properties of environmental interest (octanol–water, air–octanol, and air–water partition coefficients, and soil–water distribution coefficients, vapor pressure, and water solubility). The descriptors are suitable for use in the solvation parameter model and facilitate the estimation of a wide range of physicochemical, chromatographic, biological, and environmental properties using existing models.
Co-reporter:Colin F. Poole
Chromatographia 2012 Volume 75( Issue 21-22) pp:1343-1344
Publication Date(Web):2012 November
DOI:10.1007/s10337-012-2332-3
Co-reporter:Colin F. Poole
Chromatographia 2012 Volume 75( Issue 21-22) pp:1341-1342
Publication Date(Web):2012 November
DOI:10.1007/s10337-012-2325-2
Co-reporter:Thushara Karunasekara, Colin F. Poole
Journal of Chromatography A 2011 Volume 1218(Issue 6) pp:809-816
Publication Date(Web):11 February 2011
DOI:10.1016/j.chroma.2010.12.053
Partition coefficients for varied compounds were determined for the organic solvent–propylene carbonate biphasic partition system where the organic solvent is n-heptane, isopentyl ether or 1-octanol. These partition coefficient databases are analyzed using the solvation parameter model facilitating a quantitative comparison of the propylene carbonate-based partition systems with other totally organic partition systems. Propylene carbonate is a weak to intermediate cohesive solvent, reasonably dipolar/polarizable and hydrogen-bond basic, and weak hydrogen-bond acidic. Propylene carbonate–organic solvent systems offer a complementary approach to other totally organic biphasic partition systems for sample preparation and descriptor measurements of compounds virtually insoluble or unstable in water.
Co-reporter:Salwa K. Poole, Colin F. Poole
Journal of Chromatography A 2011 Volume 1218(Issue 19) pp:2648-2660
Publication Date(Web):13 May 2011
DOI:10.1016/j.chroma.2010.10.072
The kinetic performance of stabilized particle layers, particle membranes, and thin films for thin-layer chromatography is reviewed with a focus on how layer characteristics and experimental conditions affect the observed plate height. Forced flow and pressurized planar electrochromatography are identified as the best candidates to overcome the limited performance achieved by capillary flow for stabilized particle layers. For conventional and high performance plates band broadening is dominated by molecular diffusion at low mobile phase velocities typical of capillary flow systems and by mass transfer with a significant contribution from flow anisotropy at higher flow rates typical of forced flow systems. There are few possible changes to the structure of stabilized particle layers that would significantly improve their performance for capillary flow systems while for forced flow a number of avenues for further study are identified. New media for ultra thin-layer chromatography shows encouraging possibilities for miniaturized high performance systems but the realization of their true performance requires improvements in instrumentation for sample application and detection.
Co-reporter:Thushara Karunasekara, Colin F. Poole
Journal of Chromatography A 2011 Volume 1218(Issue 28) pp:4525-4536
Publication Date(Web):15 July 2011
DOI:10.1016/j.chroma.2011.05.023
Partition coefficients for varied compounds were determined for the organic solvent–dimethyl sulfoxide biphasic partition system where the organic solvent is n-heptane or isopentyl ether. These partition coefficient databases are analyzed using the solvation parameter model facilitating a quantitative comparison of the dimethyl sulfoxide-based partition systems with other totally organic partition systems. Dimethyl sulfoxide is a moderately cohesive solvent, reasonably dipolar/polarizable and strongly hydrogen-bond basic. Although generally considered to be non-hydrogen-bond acidic, analysis of the partition coefficient database strongly supports reclassification as a weak hydrogen-bond acid in agreement with recent literature. The system constants for the n-heptane–dimethyl sulfoxide biphasic system provide an explanation of the mechanism for the selective isolation of polycyclic aromatic compounds from mixtures containing low-polarity hydrocarbons based on the capability of the polar interactions (dipolarity/polarizability and hydrogen-bonding) to overcome the opposing cohesive forces in dimethyl sulfoxide that are absent for the interactions with hydrocarbons of low polarity. In addition, dimethyl sulfoxide–organic solvent systems afford a complementary approach to other totally organic biphasic partition systems for descriptor measurements of compounds virtually insoluble in water.
Co-reporter:Colin F. Poole;Salwa K. Poole
Journal of Separation Science 2011 Volume 34( Issue 8) pp:888-900
Publication Date(Web):
DOI:10.1002/jssc.201000724
Abstract
This article provides a summary of the development of ionic liquids as stationary phases for gas chromatography beginning with early work on packed columns that established details of the retention mechanism and established working methods to characterize selectivity differences compared with molecular stationary phases through the modern development of multi-centered cation and cross-linked ionic liquids for high-temperature applications in capillary gas chromatography. Since there are many reviews on ionic liquids dealing with all aspects of their chemical and physical properties, the emphasis in this article is placed on the role of gas chromatography played in the design of ionic liquids of low melting point, high thermal stability, high viscosity, and variable selectivity for separations. Ionic liquids provide unprecedented opportunities for extending the selectivity range and temperature-operating range of columns for gas chromatography, an area of separation science that has otherwise been almost stagnant for over a decade.
Co-reporter:Colin F. Poole
Chromatographia 2011 Volume 74( Issue 1-2) pp:
Publication Date(Web):2011 July
DOI:10.1007/s10337-011-1976-8
Co-reporter:Thushara Karunasekara
Chromatographia 2011 Volume 73( Issue 9-10) pp:
Publication Date(Web):2011 May
DOI:10.1007/s10337-011-1996-4
Partition coefficients for varied compounds were determined for the ethylene glycol–organic solvent biphasic partition system where the organic solvent is n-heptane, 1,2-dichloroethane or isopentyl ether. These partition coefficient databases are analyzed using the solvation parameter model facilitating a quantitative comparison of the ethylene glycol-based partition systems with other totally organic partition systems. Ethylene glycol is a cohesive solvent, reasonably dipolar/polarizable, strongly hydrogen-bond basic, and moderately hydrogen-bond acidic. Ethylene glycol–organic solvent systems offer a complementary approach to other totally organic biphasic partition systems for sample preparation and descriptor measurements of compounds virtually insoluble in water.
Co-reporter:Colin F. Poole
Chromatographia 2011 Volume 74( Issue 9-10) pp:
Publication Date(Web):2011 November
DOI:10.1007/s10337-011-2105-4
Co-reporter:Thushara Karunasekara, Colin F. Poole
Talanta 2011 Volume 83(Issue 4) pp:1118-1125
Publication Date(Web):30 January 2011
DOI:10.1016/j.talanta.2010.06.064
Partition coefficients for varied compounds were determined for the organic solvent–formamide biphasic partition system where the organic solvent is 1,2-dichloroethane, 1-octanol or isopentyl ether. These partition coefficient databases are analyzed using the solvation parameter model facilitating a quantitative comparison of the formamide-based partition systems with other totally organic and water-based partition systems. Formamide is shown to be a less cohesive and hydrogen-bond acidic solvent than water with similar hydrogen-bond basicity and dipolarity/polarizability. Compared with other organic solvents its higher cohesion, dipolarity/polarizability and hydrogen-bonding capability make it a useful base solvent for forming biphasic partition systems with a range of system properties obtained through variation of the counter solvent. Formamide–organic solvent systems offer a complementary approach to water-based partition systems for sample preparation and the determination of descriptors for compounds virtually insoluble in water or unstable in water.
Co-reporter:Colin F. Poole, Salwa K. Poole
Journal of Chromatography A 2010 Volume 1217(Issue 16) pp:2268-2286
Publication Date(Web):16 April 2010
DOI:10.1016/j.chroma.2009.09.011
Room temperature ionic liquids are novel solvents with a rather specific blend of physical and solution properties that makes them of interest for applications in separation science. They are good solvents for a wide range of compounds in which they behave as polar solvents. Their physical properties of note that distinguish them from conventional organic solvents are a negligible vapor pressure, high thermal stability, and relatively high viscosity. They can form biphasic systems with water or low polarity organic solvents and gases suitable for use in liquid–liquid and gas–liquid partition systems. An analysis of partition coefficients for varied compounds in these systems allows characterization of solvent selectivity using the solvation parameter model, which together with spectroscopic studies of solvent effects on probe substances, results in a detailed picture of solvent behavior. These studies indicate that the solution properties of ionic liquids are similar to those of polar organic solvents. Practical applications of ionic liquids in sample preparation include extractive distillation, aqueous biphasic systems, liquid–liquid extraction, liquid-phase microextraction, supported liquid membrane extraction, matrix solvents for headspace analysis, and micellar extraction. The specific advantages and limitations of ionic liquids in these studies is discussed with a view to defining future uses and the need not to neglect the identification of new room temperature ionic liquids with physical and solution properties tailored to the needs of specific sample preparation techniques. The defining feature of the special nature of ionic liquids is not their solution or physical properties viewed separately but their unique combinations when taken together compared with traditional organic solvents.
Co-reporter:Thushara Karunasekara
Journal of Separation Science 2010 Volume 33( Issue 8) pp:1167-1173
Publication Date(Web):
DOI:10.1002/jssc.200900797
Abstract
Partition coefficients for 84 varied compounds were determined for n-heptane–formamide biphasic partition system and used to derive a model for the distribution of neutral compounds between the n-heptane-rich and formamide-rich layers. The partition coefficients, log Kp, were correlated through the solvation parameter model giving log Kp=0.083+0.559E–2.244S–3.250A–1.614B+2.387V with a multiple correlation coefficient of 0.996, standard error of the estimate 0.139, and Fisher statistic 1791. In the model, the solute descriptors are excess molar refraction, E, dipolarity/polarizability, S, overall hydrogen-bond acidity, A, overall hydrogen-bond basicity, B, and McGowan's characteristic volume, V. The model is expected to be able to estimate further values of the partition coefficient to about 0.13 log units for the same descriptor space covered by the calibration compounds (E=−0.26–2.29, S=0–1.93, A=0–1.25, B=0.02–1.58, and V=0.78–2.50). The n-heptane–formamide partition system is shown to have different selectivity to other totally organic biphasic systems and to be suitable for estimating descriptor values for compounds of low water solubility and/or stability.
Co-reporter:Sanka N. Atapattu
Chromatographia 2010 Volume 71( Issue 3-4) pp:185-193
Publication Date(Web):2010 February
DOI:10.1365/s10337-009-1431-2
The solvation parameter model is used to establish the contribution of cohesion, dipole-type, and hydrogen-bonding interactions to the retention mechanism on Synergi Hydro-RP, Fusion-RP, and Polar-RP reversed-phase columns with methanol–water mobile phases containing from 10–70% (v/v) methanol. Large changes in relative retention on the compared columns can result from steric resistance, differences in the phase ratios, and from dewetting at low methanol compositions while changes in intermolecular interactions are responsible for smaller changes at a fixed mobile phase composition. For Synergi Hydro-RP and Polar-RP changing methanol for acetonirile is more powerful for affecting changes in retention order than changing the stationary phase. The three Synergi columns show useful selectivity differences for method development when compared with 13 other modern reversed-phase columns representing a selection of different stationary phase chemistries. The results from this study indicate the limitations of classifying reversed-phase columns by the retention of prototypical compounds to define specific retention mechanisms.
Co-reporter:Colin F. Poole, Sanka N. Atapattu, Salwa K. Poole, Andrea K. Bell
Analytica Chimica Acta 2009 Volume 652(1–2) pp:32-53
Publication Date(Web):12 October 2009
DOI:10.1016/j.aca.2009.04.038
The solvation parameter model is now well established as a useful tool for obtaining quantitative structure–property relationships for chemical, biomedical and environmental processes. The model correlates a free-energy related property of a system to six free-energy derived descriptors describing molecular properties. These molecular descriptors are defined as L (gas–liquid partition coefficient on hexadecane at 298 K), V (McGowan's characteristic volume), E (excess molar refraction), S (dipolarity/polarizability), A (hydrogen-bond acidity), and B (hydrogen-bond basicity). McGowan's characteristic volume is trivially calculated from structure and the excess molar refraction can be calculated for liquids from their refractive index and easily estimated for solids. The remaining four descriptors are derived by experiment using (largely) two-phase partitioning, chromatography, and solubility measurements. In this article, the use of gas chromatography, reversed-phase liquid chromatography, micellar electrokinetic chromatography, and two-phase partitioning for determining solute descriptors is described. A large database of experimental retention factors and partition coefficients is constructed after first applying selection tools to remove unreliable experimental values and an optimized collection of varied compounds with descriptor values suitable for calibrating chromatographic systems is presented. These optimized descriptors are demonstrated to be robust and more suitable than other groups of descriptors characterizing the separation properties of chromatographic systems.
Co-reporter:Sanka N. Atapattu, Colin F. Poole
Journal of Chromatography A 2009 Volume 1216(Issue 45) pp:7882-7888
Publication Date(Web):6 November 2009
DOI:10.1016/j.chroma.2009.09.010
The measurement of retention factors by gas chromatography on up to 15 stationary phases at several temperatures in the range 60–240 °C for each stationary phase and liquid–liquid partition coefficients in three biphasic organic solvent systems (n-hexane–acetonitrile, n-heptane–N,N-dimethylformamide, and n-heptane–2,2,2-trifluoroethanol) were used to calculate solute descriptors for 28 semivolatile linear and cyclic organosilicon compounds for use in the solvation parameter model. Regression analysis for oligomeric compounds allowed the descriptor values for the dimethylsiloxane, diethylsiloxane, methylvinylsiloxane, and methylhydrosiloxane monomer groups to be estimated. These monomer groups contribute significantly to the hydrogen-bond basicity (B descriptor) and cavity formation and dispersion interactions (L and V descriptors) of oligomeric organosilicon compounds, are non-hydrogen-bond acidic (A descriptor = 0), are slightly less dipolar/polarizable than an n-alkane (S descriptors are negative and close to zero), and bind electron lone pairs more tightly than an n-alkane (E descriptor is small and negative). The semivolatile organosilicon compounds with polar functional groups in their side chain demonstrate a much wider range of selective intermolecular interactions than alkylsiloxanes and have solvation properties closer to those of polar organic compounds.
Co-reporter:Sanka N. Atapattu, Kimberly Eggers, Colin F. Poole, Waruna Kiridena, Wladyslaw W. Koziol
Journal of Chromatography A 2009 Volume 1216(Issue 10) pp:1640-1649
Publication Date(Web):6 March 2009
DOI:10.1016/j.chroma.2008.11.057
The solvation parameter model is used to characterize the separation properties of four open-tubular columns for gas chromatography at low and intermediate column temperatures covering the range 60–240 °C. Solute descriptors for compounds suitable for characterizing columns over the intermediate temperature range are optimized using an iterative procedure. These compounds, and those previously recommended for the lower temperature range, are used to provide system constant maps for Rxi-5Sil MS, Rxi-17, Rtx-TNT and Rtx-TNT2 columns suitable for merging with a system constants database with entries for more than 50 columns. The Rxi-5Sil MS column is shown to have separation properties similar to the silphenylene–dimethylsiloxane copolymer stationary phase (DB-5ms) but these two columns are not selectivity equivalent. The Rxi-17 column has similar separation properties to the Rxi-50 column but is not selectivity equivalent to it. Rxi-17 is a poly(dimethyldiphenylsiloxane) stationary phase containing 50% diphenylsiloxane monomer and Rxi-50 a poly(methylphenylsiloxane) stationary phase with the same nominal composition but a different monomer structure. The difference in monomer structure results in only small changes in selectivity, and for all but the most demanding separations, the columns are interchangeable. The application-specific column (energetic materials) Rtx-TNT is shown to be selectivity equivalent to columns coated with the poly(dimethyldiphenylsiloxane) stationary phases containing 5% diphenylsiloxane monomer. The Rtx-TNT2 column is selectivity equivalent to the proprietary Rtx-OPPesticides column. Rtx-OPPesticides is a low bleed stationary phase, possibly based on silarylene–siloxane chemistry, with a composition designed to mimic the separation properties of the poly(dimethylmethyltrifluoropropylsiloxane) stationary phases containing 35% methyltrifluoropropylsiloxane monomer. Selectivity equivalence of columns is determined by the statistical agreement in system constants at 20 °C intervals over the full temperature range from 60 to 240 °C, and by the construction of correlation plots for the retention factors of varied compounds for the same temperature intervals.
Co-reporter:Colin F. Poole, Salwa K. Poole
Journal of Chromatography A 2009 Volume 1216(Issue 10) pp:1530-1550
Publication Date(Web):6 March 2009
DOI:10.1016/j.chroma.2008.10.092
The connection between the observable output in column chromatography (retention time, retention volume, retention factor, separation factor, etc.) and system properties (hold-up volume, pressure, temperature, isotherm behavior, etc.) is discussed from a practical and mechanistic perspective for gas–liquid chromatography, reversed-phase liquid chromatography, supercritical fluid chromatography, micellar electrokinetic chromatography, and capillary electrochromatography. The unifying feature of these techniques is that retention can be described by a partition model, although not always exclusively. When over simplistic system models are used to explain variation in retention parameters they frequently mask the true reasons for poor repeatability and difficulties in transfer between system. Methods employing relative retention afford higher precision but may contain residual uncorrected errors. For those systems with several separate mechanisms contributing to retention the effective retention parameters can no longer be interpreted by simple partition models. The broadly based and practically focused material in this article affords an illustration of the often complicated relationship between system properties and retention, and the dangers that lurk in simplified retention models if the validity of their underlining approximations is not appropriate for the system under study.
Co-reporter:Sanka N. Atapattu and Colin F. Poole
Environmental Science: Nano 2009 vol. 11(Issue 4) pp:815-822
Publication Date(Web):29 Jan 2009
DOI:10.1039/B818063F
The solvation parameter model is used to characterize interactions responsible for the sorption of varied organic compounds by diesel soot and atmospheric aerosols at 15 °C and 50% relative humidity. Individual models are obtained for eight aerosol samples characterized as urban, suburban, rural and coastal. Combining the individual aerosol models resulted in a general aerosol model with only a minor loss of modeling power for alkanecarboxylic acids and low-molecular weight alcohols compared with the individual models. A second group of compounds identified as weak nitrogen-containing bases were consistent outliers to all models most likely due to participation in ion-exchange interactions not considered by the models. The diesel soot and atmospheric aerosols exhibit similar characteristics with respect to their sorption interactions although differences in relative magnitude allow the two particle types to be easily distinguished. Sorption interactions are favored by strong dispersion interactions for both particle types. Of note is the strong hydrogen-bond basicity and relatively weak hydrogen-bond acidity of these materials. The particles are quite dipolar/polarizable and slightly electron lone pair repulsive. The sorption properties of the atmospheric aerosols are influenced by the relative humidity, in particular, the aerosols become significantly more hydrogen-bond acidic at high relative humidity most likely due to incorporation of increasing amounts of condensed or film water in the aerosol phase. Dividing the data into training and test sets suggests that the proposed models are capable of estimating distribution constants (log K) to about 0.20 log units for diesel soot (n = 84) and 0.14 log units for the general atmospheric aerosol model (n = 385) where n indicates the number of compounds included in the model.
Co-reporter:Salwa K. Poole
Journal of Separation Science 2008 Volume 31( Issue 6-7) pp:1118-1123
Publication Date(Web):
DOI:10.1002/jssc.200700546
Abstract
A database of system constants for 32 open-tubular columns at 100°C is used to identify stationary phases for obtaining a wide selectivity space in comprehensive GC. Three parameters based on the Euclidean distance (D-parameter) or vectors (d-parameter and cosθ) in hyperspace are used to establish the chemical similarity and retention correlation as an inverse scale of selectivity differences. It is shown that the poly(methyloctylsiloxane) stationary phase is the best candidate for a low-selectivity stationary phase and affords a wider selectivity space when combined with a selective polar stationary phase than poly(dimethylsiloxanes). The most suitable polar stationary phases are poly(ethylene glycols) or bis(cyanopropylsiloxane-co-silarylenes and to a lesser extent poly(methyltrifluoropropylsiloxanes). No systems are truly orthogonal but angles between individual stationary phase vectors of about 75° are possible by choosing the correct combination of stationary phases.
Co-reporter:Waruna Kiridena;Sanka N. Atapattu;Wladyslaw W. Koziol
Chromatographia 2008 Volume 68( Issue 7-8) pp:491-500
Publication Date(Web):2008 October
DOI:10.1365/s10337-008-0778-0
Differences in the system constants of the solvation parameter model and retention factor correlation plots for varied solutes are used to study the retention mechanism on XBridge C8, XBridge Phenyl and XTerra Phenyl stationary phases with acetonitrile–water and methanol–water mobile phases containing from 10 to 70% (v/v) organic solvent. These stationary phases are compared with XBridge C18 and XBridge Shield RP18 characterized in an earlier report using the same protocol. The XBridge stationary phases are all quite similar in their retention properties with larger difference in absolute retention explained by differences in cohesion and the phase ratio, mainly, and smaller changes in relative retention (selectivity) by the differences in individual system constants and their variation with mobile phase type and composition. None of the XBridge stationary phases are selectivity equivalent but XBridge C18 and XBridge Shield RP18 have similar separation properties, likewise so do XBridge C8 and XBridge Phenyl, while the differences between the two groups of two stationary phases is greater than the difference within either group. The limited range of changes in selectivity is demonstrated by the high coefficient of determination (>0.98) for plots of the retention factors for varied compounds on the different XBridge phases with the same mobile phase composition.
Co-reporter:Waruna Kiridena;Sanka N. Atapattu;Wladyslaw W. Koziol
Chromatographia 2008 Volume 68( Issue 1-2) pp:11-17
Publication Date(Web):2008 July
DOI:10.1365/s10337-008-0644-0
The solvation parameter model is used to elucidate the retention mechanism of neutral organic compounds on the octadecylsiloxane-bonded silica stationary phase SunFire C18 with acetonitrile–water, methanol–water and tetrahydrofuran–water mobile phases containing from 10 to 70% (v/v) organic solvent. The dominant factors that increase retention are solute size and electron lone pair interactions while polar interactions reduce retention. The contribution of solvent type on selectivity is discussed in relation to its affect on the system constants of the solvation parameter model. Steric repulsion is shown not to affect the retention mechansim for a wide range of compounds and electrostatic interactions are shown to be weak and only important for mobile phases containing acetonitrile. Dewetting affects the retention mechanism of acetonitrile–water mobile phase compositions containing less than 30% (v/v) acetonitrile and for tetrahydrofuran–water compositions containing less than 20% (v/v) tetrahydrofuran. SunFire C18 should be suitable for determining the S, A and B solute descriptors for neutral compounds and weak bases using reversed-phase liquid chromatography.
Co-reporter:Hamid Ahmed, Colin F. Poole, Gary E. Kozerski
Journal of Chromatography A 2007 Volume 1169(1–2) pp:179-192
Publication Date(Web):26 October 2007
DOI:10.1016/j.chroma.2007.09.001
Measurements of retention factors by gas chromatography on up to 10 complementary stationary phases at up to 5 temperatures for each stationary phase and liquid–liquid partition coefficients in three biphasic organic solvent systems (n-hexane-acetonitrile, n-heptane-N,N-dimethylformamide and n-heptane-2,2,2-trifluoroethanol) were used to estimate solute descriptors for 54 organosilicon compounds for use in the solvation parameter model. Many of the E descriptor values (electron lone pair interactions) are negative for simple siloxanes and silanes indicating that these compound bind electron lone pairs more tightly than n-alkanes. Silanes and siloxanes with alkyl groups have near zero dipolarity/polarizability (S descriptor). The S descriptor is only modest for simple phenylsilanes, silazanes, silanols, orthosilicates, and alkoxides. All organosilicon compounds with silicon-oxygen bonds are reasonably strong hydrogen-bond bases (B descriptor) but only the silanol group is a reasonably strong hydrogen-bond acid (A descriptor). Silanes (SiH) and silazanes (SiNHSi) are weak hydrogen-bond acids. Cavity formation and dispersion interactions (V or L descriptor) are often the main component of solvation models for siloxanes and silanes that have simple alkyl and aromatic substituents. A number of physicochemical properties (vapor pressure, aqueous solubility, biphasic partition coefficients, sorption coefficients, etc.) for linear and cyclic dimethylsiloxanes can be reliably predicted from their descriptors in established models for organic compounds.
Co-reporter:Waruna Kiridena;Jing Qian;Wladyslaw W. Koziol
Journal of Separation Science 2007 Volume 30(Issue 5) pp:740-745
Publication Date(Web):2 MAR 2007
DOI:10.1002/jssc.200600453
The solvation parameter model is used to characterize the separation properties of the polar stationary phases EC-Wax and PAG with a poly(ethylene oxide) backbone (substituted with propylene oxide in the case of PAG) and the cyanopropyl-substituted polysilphenylene–siloxane stationary phase BPX90 at five equally spaced temperatures between 60 and 140°C. The separation characteristics of these stationary phases are compared to four PEG and two poly(cyanopropylsiloxane) stationary phases (HP-20M, HP-Innowax, SolGel-Wax, DB-WAXetr, HP-88, and SP-2340) characterized in the same way. The database of system constants for these polar stationary phases is used to provide insight into the separation mechanism for fatty acid methyl esters and to determine selectivity differences that can be expected for generically similar stationary phase types. The discussion is not structured to indicate which stationary phase should be used for a particular separation but to provide a general framework to demonstrate the relationship between the retention mechanism and stationary phase chemistry.
Co-reporter:Jing Qian
Journal of Separation Science 2007 Volume 30(Issue 14) pp:2326-2331
Publication Date(Web):2 AUG 2007
DOI:10.1002/jssc.200700175
Partition coefficients for 86 varied compounds were determined for the chloroform–methanol–water (8:4:3 v/v) biphasic partition system and used to derive a model for the distribution of neutral compounds between the water-rich and chloroform-rich layers. The partition coefficients, log Kp, were correlated through the solvation parameter model giving log Kp = 1.336 – 0.014E + 0.413S + 1.583A + 1.344B – 1.378V with a multiple correlation coefficient of 0.973, standard error of the estimate 0.151, and Fischer statistic 286. In the model the solute descriptors are excess molar refraction, E, dipolarity/polarizability, S, overall hydrogen-bond acidity, A, overall hydrogen-bond basicity, B, and McGowan's characteristic volume, V. The model is expected to be able to estimate further values of the partition coefficient to about 0.13 log units. The chloroform–methanol–water partition system is shown to have different selectivities to 44 common water–organic solvent and totally organic biphasic partition systems.
Co-reporter:C. F. Poole;H. Ahmed;W. Kiridena;C. DeKay;W. W. Koziol
Chromatographia 2007 Volume 65( Issue 3-4) pp:127-139
Publication Date(Web):2007 February
DOI:10.1365/s10337-006-0131-4
The solvation parameter model is used to elucidate the retention mechanism on a perfluorohexylpropylsiloxane-bonded (Fluophase RP) and octadecylsiloxane-bonded (Betasil C18) stationary phases based on the same silica substrate with acetonitrile–water and methanol–water mobile phase compositions. Dewetting affects the retention properties of Fluophase RP at mobile phase compositions containing less than 20% (v/v) acetonitrile or 40% (v/v) methanol. It results in a loss of retention due to an unfavorable change in the phase ratio as well as changes in specific intermolecular interactions. Steric repulsion reduces retention of bulky solutes on fully solvated Betasil C18 with methanol–water (but not acetonitrile–water) mobile phase compositions but is not important for Fluophase RP. The retention of weak bases is affected by ion-exchange interactions on Fluophase RP with acetonitrile–water, and to a lesser extent, methanol-water mobile phases but these are weak at best for Betasil C18. The system constants of the solvation parameter model and retention factor scatter plots are used to compare selectivity differences for Fluophase RP, Betasil C18 and a perfluorophenylpropylsiloxane-bonded silica stationary phase Discovery HS F5 for conditions where incomplete solvation, steric repulsion and ion-exchange do not significantly contribute to the retention mechanism. Lower retention on Fluophase RP results from weaker dispersion and/or higher cohesion moderated to different extents by polar interactions since solvated Fluophase RP is a stronger hydrogen-bond acid and more dipolar/polarizable than Betasil C18. Retention factors for acetonitrile–water mobile phases are highly correlated for Fluophase RP and Betasil C18 except for compounds with a large excess molar refraction and weak hydrogen-bonding capability. Selectivity differences are more significant for methanol–water mobile phases. Retention factors on Fluophase RP are strongly correlated with those on Discovery HSF5 for acetonitrile–water mobile phases while methanol–water mobile phases retention on Fluophase RP is a poor predictor of the retention order on Discovery HS F5.
Co-reporter:Waruna Kiridena;Sanka N. Atapattu;Jing Qian
Chromatographia 2007 Volume 66( Issue 7-8) pp:453-460
Publication Date(Web):2007 October
DOI:10.1365/s10337-007-0355-y
Differences in the system constants of the solvation parameter model, discontinuities in retention factor plots (log k against volume fraction of organic solvent) and retention factor correlation plots are used to study the retention mechanism on XTerra MS C18, XBridge C18 and XBridge Shield RP18 stationary phases with acetonitrile–water and methanol–water mobile phases containing from 10 to 70% (v/v) organic solvent. Wetting of XBridge C18 at 10 and 20% (v/v) acetonitrile is incomplete and is responsible for small changes in the retention mechanism. The intermolecular interactions responsible for retention on XTerra MS C18 and XBridge C18 are similar with minor differences in cavity formation and hydrogen-bonding interactions responsible for small selectivity differences. On the other hand, for bulky solutes there are large changes in retention at low volume fractions of organic solvent (<40% v/v) associated with steric repulsion on the XTerra MS C18 stationary phases that is absent for XBridge C18. Selectivity differences are more apparent for XBridge C18 and XBridge Shield RP18. For acetonitrile-water mobile phases cavity formation in the solvated XBridge Shield RP18 is slightly more difficult and hydrogen-bond acid and base interactions are more important than for XBridge C18. With methanol–water mobile phases it becomes slightly easier to form a cavity in the solvated XBridge RP18 compared with XBridge C18. In addition, the methanol-water solvated XBridge RP18 is a stronger hydrogen-bond base and more dipolar/polarizable than XBridge C18. These variations in selectivity justify the use of XBridge C18 and XBridge Shield RP18 as complementary stationary phases for method development.
Co-reporter:Colin F. Poole, Waruna Kiridena, Colleen DeKay, Wladyslaw W. Koziol, Renae D. Rosencrans
Journal of Chromatography A 2006 Volume 1115(1–2) pp:133-141
Publication Date(Web):19 May 2006
DOI:10.1016/j.chroma.2006.02.089
Plots of the retention factor against mobile phase composition were used to organize a varied group of solutes into three categories according to their retention mechanism on an octadecylsiloxane-bonded silica stationary phase HyPURITY C18 with methanol–water and acetonitrile–water mobile phase compositions containing 10–70% (v/v) organic solvent. The solutes in category 1 could be fit to a general retention model, Eq. (2), and exhibited normal retention behavior for the full composition range. The solutes in category 2 exhibited normal retention behavior at high organic solvent composition with a discontinuity at low organic solvent compositions. The solutes in category 3 exhibited a pronounced step or plateau in the middle region of the retention plots with a retention mechanism similar to category 1 solutes at mobile phase compositions after the discontinuity and a different retention mechanism before the discontinuity. Selecting solutes and appropriate composition ranges from the three categories where a single retention mechanism was operative allowed modeling of the experimental retention factors using the solvation parameter model. These models were then used to predict retention factors for solutes not included in the models. The overwhelming number of residual values [log k (experimental) − log k (model predicted)] were negative and could be explained by contributions from steric repulsion, defined as the inability of the solute to insert itself fully into the stationary phase because of its bulkiness (i.e., volume and/or shape). Steric repulsion is shown to strongly depend on the mobile phase composition and was more significant for mobile phases with a low volume fraction of organic solvent in general and for mobile phases containing methanol rather than acetonitrile. For mobile phases containing less than about 20 % (v/v) organic solvent the mobile phase was unable to completely wet the stationary phase resulting in a significant change in the phase ratio and for acetonitrile (but less so methanol) changes in the solvation environment indicated by a discontinuity in the system maps.
Co-reporter:Waruna Kiridena, Colleen DeKay, Cheryl C. Patchett, Wladyslaw W. Koziol, Jing Qian, Colin F. Poole
Journal of Chromatography A 2006 Volume 1128(1–2) pp:228-235
Publication Date(Web):22 September 2006
DOI:10.1016/j.chroma.2006.06.068
The solvation parameter model is used to characterize the retention properties of four application-specific open-tubular columns (Rtx-CLPesticides, Rtx-OPPesticides, Rtx-Dioxin and Rtx-Dioxin2) at five equally spaced temperatures over the range 60–140 °C. Cluster analysis is used to compare the system constants to a database of forty open-tubular columns characterized according to the same method. System constants differences and retention factor correlation plots are then used to determine selectivity differences between the application-specific columns and their nearest neighbors identified by cluster analysis. The Rtx-CLPesticides and Rtx-OPPesticides columns are shown to belong to the selectivity group containing poly(dimethylmethyltrifluoroprpylsiloxane) stationary phases with Rtx-OPPesticides having a similar selectivity to a poly(dimethylmethyltrifluoropropylsiloxane) stationary phase containing 20% methyltrifluoropropylsiloxane monomer (DB-200) and Rtx-CLPesticides separation properties for a stationary phase containing less than 20% methyltrifluoropropylsiloxane monomer. The Rtx-Dioxin and Rtx-Dioxin2 columns are located in the selectivity group dominated by the poly(dimethyldiphenylsiloxane) stationary phases containing less than 20% diphenylsiloxane monomer. The Rtx-Dioxin and Rtx-Dioxin2 columns are shown to be selectivity equivalent to a (5% phenyl) carborane-siloxane copolymer stationary phase (Stx-500) and a second generation silarylene-siloxane copolymer stationary phase containing dimethylsiloxane and diphenylsiloxane monomers (DB-XLB), respectively.
Co-reporter:Colin F. Poole, Jing Qian, Waruna Kiridena, Colleen DeKay, Wladyslaw W. Koziol
Journal of Chromatography A 2006 Volume 1134(1–2) pp:284-290
Publication Date(Web):17 November 2006
DOI:10.1016/j.chroma.2006.08.092
The solvation parameter model is used to characterize the separation characteristics of two application-specific open-tubular columns (Rtx-Volatiles and Rtx-VGC) and a general purpose column for the separation of volatile organic compounds (DB-WAXetr) at five equally spaced temperatures over the range 60–140 °C. System constant differences and retention factor correlation plots are then used to determine selectivity differences between the above columns and their closest neighbors in a large database of system constants and retention factors for forty-four open-tubular columns. The Rtx-Volatiles column is shown to have separation characteristics predicted for a poly(dimethyldiphenylsiloxane) stationary phase containing about 16% diphenylsiloxane monomer. The Rtx-VGC column has separation properties similar to the poly(cyanopropylphenyldimethylsiloxane) stationary phase containing 14% cyanopropylphenylsiloxane monomer DB-1701 for non-polar and dipolar/polarizable compounds but significantly different characteristics for the separation of hydrogen-bond acids. For all practical purposes the DB-WAXetr column is shown to be selectivity equivalent to poly(ethylene glycol) columns prepared using different chemistries for bonding and immobilizing the stationary phase. Principal component analysis and cluster analysis are then used to classify the system constants for the above columns and a sub-database of eleven open-tubular columns (DB-1, HP-5, DB-VRX, Rtx-20, DB-35, Rtx-50, Rtx-65, DB-1301, DB-1701, DB-200, and DB-624) commonly used for the separation of volatile organic compounds. A rationale basis for column selection based on differences in intermolecular interactions is presented as an aid to method development for the separation of volatile organic compounds.
Co-reporter:Colin F. Poole, Hamid Ahmed, Waruna Kiridena, Cheryl C. Patchett, Wladyslaw W. Koziol
Journal of Chromatography A 2006 Volume 1104(1–2) pp:299-312
Publication Date(Web):3 February 2006
DOI:10.1016/j.chroma.2005.11.062
An iteration procedure is used to calculate revised solute descriptors for 103 varied compounds suitable for characterizing the retention properties of stationary phases for gas chromatography using the solvation parameter model. The iteration procedure utilizes a database of retention factors obtained on up to 39 open-tubular columns and up to five temperatures in the range 60–140 °C for the 103 solutes. The average of the standard deviation [Σ(log kexp – log kcalc)2/(nc – 1)]0.5 where log kexp is the experimental retention factor, log kcalc the model predicted retention factor, and nc the total number of retention factors) on all columns is 0.018 for the revised solute descriptors compared with 0.045 for the original values. When used to characterize the retention properties of six open-tubular columns selected to represent different selectivity groups the revised solute descriptors afford improved values for the multiple correlation coefficient and standard deviations of the system constants, and about a three-fold improvement in the standard error of the estimate compared with the original solute descriptors. The revised solute descriptors were used to model retention on the carborane–siloxane copolymer stationary phase Stx-500. This phase has low cohesion, is weakly electron lone pair repulsive, weakly dipolar/polarizable, and weakly hydrogen-bond basic. It has no hydrogen-bond acidity. Its separation properties are similar to those of the poly(diphenyldimethylsiloxane) stationary phases containing 5% diphenylsiloxane monomer, but it is not selectivity equivalent to these phases, being more dipolar/polarizable and a weaker hydrogen-bond base.
Co-reporter:Hamid Ahmed
Journal of Separation Science 2006 Volume 29(Issue 14) pp:2158-2165
Publication Date(Web):1 SEP 2006
DOI:10.1002/jssc.200600131
Partition coefficients for a number of varied compounds were determined for the n-heptane–methanol and n-heptane–DMF partition systems and used to derive a general model for the distribution of neutral compounds in the biphasic systems. The partition coefficient, log Kp, was correlated through the solvation parameter model giving log Kp = –0.056 + 0.164E–0.620S–1.337A–0.957B + 0.507V for the n-heptane-methanol system with a multiple correlation coefficient of 0.986, standard error of the estimate 0.086, and Fischer statistic 413 for 65 compounds. For n-heptane–DMF, the model is log Kp = 0.065 + 0.030E–1.405S–2.039A–0.806B + 0.721V with a multiple correlation coefficient of 0.991, standard error of the estimate 0.080, and Fischer statistic 560 for 59 compounds. In the models the solute descriptors are excess molar refraction E, dipolarity/polarizability S, overall hydrogen bond acidity, and basicity A and B, respectively, and McGowan's characteristic volume V. Either model is expected to be able to estimate further values of the partition coefficient to about 0.08 log units and is applicable to a wide range of compounds. Applications include the choice of partitioning systems for sample clean-up, countercurrent chromatography, and estimation of solute descriptors for water insoluble or unstable compounds.
Co-reporter:Waruna Kiridena;Cheryl C. Patchett;Hamid Ahmed;Wladyslaw W. Koziol
Journal of Separation Science 2006 Volume 29(Issue 2) pp:211-217
Publication Date(Web):19 JAN 2006
DOI:10.1002/jssc.200500274
The solvation parameter model is used to characterize the retention properties of five open-tubular column stationary phases (ZB-5 ms, DB-5 ms, DB-XLB, DB-17 ms, and DB-35 ms) based on silarylene-siloxane copolymer chemistries at five equally spaced temperatures over the range 60–140°C. System constant differences and regression models for varied compounds are used to establish the selectivity equivalence of the silarylene-siloxane copolymer stationary phases and to compare their separation characteristics with poly(dimethyldiphenylsiloxane) stationary phases containing a nominally similar concentration of phenyl groups. These studies demonstrate that ZB-5 ms and DB-5 ms are selectivity equivalent. DB-XLB is significantly more dipolar and polarizable than DB-5 ms. In general terms, the silarylene-siloxane copolymer stationary phases are slightly less cohesive and more dipolar and polarizable with similar hydrogen-bond basicity to the poly(dimethyldiphenylsiloxane) stationary phases they were designed to replace. None of the silarylene-siloxane copolymer or poly(dimethyldiphenylsiloxane) stationary phases are hydrogen-bond acidic. Selectivity differences between the two types of stationary phase are temperature dependent and tend to be smaller at higher temperatures within the temperature range studied. Consequently, selectivity differences cannot be globalized without reference to the temperature for the comparison.
Co-reporter:Waruna Kiridena, Cheryl C. Patchett, Wladyslaw W. Koziol, Colin F. Poole
Journal of Chromatography A 2005 Volume 1081(Issue 2) pp:248-254
Publication Date(Web):22 July 2005
DOI:10.1016/j.chroma.2005.05.062
The solvation parameter model is used to characterize the retention properties of the bis(cyanopropylsiloxane)-co-methylsilarylene, HP-88, and poly(siloxane), Rtx-440, stationary phases over the temperature range 60–140 °C. HP-88 is among the most cohesive, dipolar/polarizable and hydrogen-bond basic of stationary phases for open-tubular column gas chromatography. It has no hydrogen-bond acidity or capacity for electron lone pair interactions. It exhibits similar selectivity to the poly(cyanopropylsiloxane) stationary phase SP-2340. Rtx-440 is a low-polarity, low-cohesion stationary phase with a moderate capacity for dipolar/polarizable and hydrogen-bond base interactions. It has no hydrogen-bond acidity and possesses weak electron lone pair interactions. It has unique selectivity when compared against a system constants database for 28 common stationary phase compositions. Cluster analysis indicated that the poly(cyanopropylphenyldimethylsiloxane) stationary phase containing 6% cyanopropylphenylsiloxane monomer, DB-1301, the poly(dimethyldiphenylsiloxane) stationary phase containing 20% diphenylsiloxane monomer, Rtx-20, the poly(siloxane) stationary phase of unknown composition, DB-624, and DX-1 [a mixture of poly(dimethylsiloxane) and poly(ethylene glycol) 9:1] are the closest selectivity matches in the database. The selectivity of DB-1301 and Rtx-440 are very similar for solutes with weak hydrogen-bond acidity allowing one stationary phase to be substituted for the other with likely success. For strong hydrogen-bond acids, such as phenols, DB-1301 and Rtx-440 exhibit different selectivity.
Co-reporter:Colin F. Poole
Environmental Science: Nano 2005 vol. 7(Issue 6) pp:577-580
Publication Date(Web):22 Apr 2005
DOI:10.1039/B501776A
The solvation parameter model is used to characterize interactions responsible for adsorption at the gas–water interface for bulk water at 15 and 25 °C, snow at −6.8 °C, mineral-supported water films (alumina, calcium carbonate and quartz) at 15 °C, and dry soil at 15 °C. The mineral-supported water films and dry soil adsorption data are modeled at different relative humidities in the range 40–99%. The models produce satisfactory results with standard errors of the estimate of 0.12 to 0.17 for regression of the model predicted adsorption equilibrium constants against the experimental values (range for equilibrium constants −2 to −7 log units). The water surface is polar with a significant capacity for dipole-type and hydrogen-bonding interactions. In addition, it is strongly electron lone pair repulsive. Dispersion interactions favor adsorption at the water surface. Mineral-supported water films at relative humidities greater than 40% demonstrate adsorption properties similar to bulk water. The adsorption characteristics, however, depend on the relative humidity and the nature of the support. In the case of dry soil the adsorption properties at different relative humidities cannot simply be explained by adsorption of a water film covering the soil surface and the changes in adsorption characteristics with relative humidity are more complex than the mineral-supported water films.
Co-reporter:Cheryl C. Patchett;Wladyslaw W. Koziol;Waruna Kiridena
Journal of Separation Science 2004 Volume 27(Issue 15‐16) pp:1333-1338
Publication Date(Web):11 NOV 2004
DOI:10.1002/jssc.200401862
The solvation parameter model is used to characterize the selectivity of DB-608 and DB-624 open-tubular columns at five equally spaced temperatures over the range 60 to 140°C. The system constants for the DB-608 and DB-624 columns were used as selectivity parameters to search a database of open-tubular columns to identify columns with similar selectivity. The search was refined using the absolute deviation of the system constants and retention factor regression models for varied compounds. For method development it is shown that the selectivity of the poly(cyanopropylphenyldimethylsiloxane) stationary phase containing 6% cyanopropylphenylsiloxane monomer (DB-1301) is equivalent to DB-624 and the poly(dimethyldiphenylsiloxane) stationary phases containing either 50 or 65% diphenylsiloxane monomer (Rtx-50 and Rtx-65) are suitable choices for DB-608.
Co-reporter:Mohamed I. Nawas;Wladyslaw W. Koziol;Waruna Kiridena
Journal of Separation Science 2003 Volume 26(Issue 12‐13) pp:1111-1118
Publication Date(Web):18 AUG 2003
DOI:10.1002/jssc.200301518
The solvation parameter model is used to identify contributions from intermolecular interactions responsible for non-specific retention in gas chromatography for three dissolved β-cyclodextrin derivatives in a poly(cyanopropylphenyldimethylsiloxane) stationary phase. The cyclodextrins are permethylated β-cyclodextrin (Cyclodex-B), heptakis(2,3-di-O-methyl-6-O-t-butyldimethylsilyl)-β-cyclodextrin (CycloSil-B) and heptakis(2,3-di-O-acetoxy-6-O-t-butyldimethylsilyl)-β-cyclodextrin (Rt-βDEXsa). Taking DB-1701 as a reference phase for the poly(cyanopropylphenyldimethylsiloxane) solvent, it is shown that the dominant interactions for the cyclodextrin derivatives are associated with their hydrogen-bond basicity and capacity for dipole-type interactions. None of the cyclodextrin derivatives are hydrogen-bond acids and all are weakly electron lone pair repulsive. The cohesive properties of the dissolved phases are similar to those of the solvent, except for Rt-βDEXsa, which is significantly more cohesive. Also, Rt-βDEXsa shows significant inclusion complexation for the compounds used to determine the system constants of the solvation parameter model resulting in poor statistical models, suitable only for qualitative interpretation. The Cyclodex-B and CycloSil-B columns are compared to a database of 23 open-tubular column stationary phases possessing similar selectivity to each other but different selectivity for non-specific interactions to the other stationary phase types.
Co-reporter:Colin F. Poole, Salwa K. Poole
Journal of Chromatography A 2002 Volume 965(1–2) pp:263-299
Publication Date(Web):2 August 2002
DOI:10.1016/S0021-9673(01)01361-9
The solvation parameter model is a useful tool for delineating the contribution of defined intermolecular interactions to retention of neutral molecules in separation systems based on a solute equilibrium between a gas, liquid or fluid mobile phase and a liquid or solid stationary phase. The free energy for this process is decomposed into contributions for cavity formation and the set up of intermolecular interactions identified as dispersion, electron lone pair, dipole-type and hydrogen bonding. The relative contribution of these interactions is indicated by a series of system constants determined by the difference of the defined interaction in the two phases. The interpretation of these system constants as a function of experimental factors that affect retention in the chromatographic system provides the connection between relative retention (selectivity) and the control variables for the separation system. To aid in the understanding of these processes we perform an analysis of system constants for gas chromatography, liquid chromatography, supercritical fluid chromatography and micellar electrokinetic chromatography as a function of different experimental variables as a step towards gaining a theoretical understanding of selectivity optimization for method development.
Co-reporter:Waruna Kiridena, Colin F. Poole and Wiadyslaw W. Koziol
Analyst 2002 vol. 127(Issue 12) pp:1608-1613
Publication Date(Web):31 Oct 2002
DOI:10.1039/B209205K
The solvation parameter model is used to determine the system constants for two sol-gel coated open-tubular columns at five equally spaced temperatures in the range 60–140 °C. Differences in the system constants as a function of temperature are used to determine the affect of sol-gel structure on the selectivity of SolGel-1™ and SolGel-Wax™ columns compared with conventionally coated and immobilized poly(dimethylsiloxane) and poly(ethylene glycol) stationary phases. The sol-gel columns should be suitable for similar separations to those presently performed on conventional immobilized liquid film columns of the same type but selectivity differences for polar compounds, which depend on temperature, should be anticipated.
Co-reporter:Diana M. Cimpean and Colin F. Poole
Analyst 2002 vol. 127(Issue 6) pp:724-729
Publication Date(Web):13 May 2002
DOI:10.1039/B202010F
A systematic approach for identifing surrogate chromatographic models for biopartitioning processes is described. The method is based on a comparison of the system constant ratios of the solvation parameter model for biopartitioning processes and a database of system constant ratios for reversed-phase liquid chromatographic and micellar electrokinetic chromatographic systems compiled from literature sources. An acceptance filter of ⩽0.2 is applied for each difference in system constant ratio for the compared systems to provide a reasonable probability of success without outputting too many systems with limited predictive properties. Surrogate chromatographic models identified for the non-specific toxicity of neutral organic compounds to the fathead minnow and the soil–water distribution constant are tested by construction of a correlation model for the characteristic property of the biological process and the chromatographic retention factors for a structurally varied
group of compounds. Although these models are not the best that could be obtained based on ranking of the differences in system constant ratios the predictive ability of the correlation models is suitable for typical applications and similar to the accepted uncertainty in the measurements of the biological property. Retention factors on the immobilized artificial membrane column (IAM PC DD 2) with 10% (v/v) methanol–water as mobile phase are able to estimate non-specific toxicity to the fathead minnow with a standard error (SE) of 0.22 log units and coefficient of determination (r2) of 0.97 for 31 compounds. Retention factors on a Bakerbond DIOL column with 20% (v/v) acetonitrile–water as mobile phase are able to estimate the soil–water distribution constant with an SE of 0.38 log units and r2 = 0.88 for 59 compounds. Other potential surrogate chromatographic models are identified for non-specific toxicity to the guppy, tadpole, Vibrio
fischeri and Terahymena pyriformis as well as the plant cuticle matrix–water distribution constant. On the other hand reversed-phase chromatographic systems seem poorly suited for estimating intestinal absorption and the blood–brain distribution constant.
Co-reporter:Waruna Kiridena;Wladyslaw W. Koziol;Mohamed I. Nawas
Journal of Separation Science 2002 Volume 25(Issue 12) pp:749-759
Publication Date(Web):14 AUG 2002
DOI:10.1002/1615-9314(20020801)25:12<749::AID-JSSC749>3.0.CO;2-0
The solvation parameter model is used to determine the system constants for three columns containing mixtures of poly(dimethylsiloxane) and poly(ethylene glycol) and a poly(cyanopropylphenyldimethylsiloxane) containing 6% of cyanopropylphenylsiloxane monomer at five equally spaced temperatures in the range 60–140°C. Together with literature data for a poly(dimethylsiloxane) and a poly(ethylene glycol) stationary phase the influence of temperature and composition on selectivity is studied for mixing ratios of 0 to 1 poly(ethylene glycol) for the temperature range 60–140°C. Using literature data for two poly(cyanopropylphenyldimethylsiloxane) stationary phases containing 14% and 50% of cyanopropylphenylsiloxane monomer groups the influence of temperature and replacing dimethylsiloxane monomer groups by cyanopropylphenylsiloxane groups on selectivity is studied for incorporation of 0 to 0.5 cyanopropylphenylsiloxane groups over the temperature range 60–140°C. Addition of poly(ethylene glycol) or introduction of cyanopropylphenylsiloxane monomer groups into a poly(dimethylsiloxane) influences selectivity through an increase in dipolarity/polarizability, hydrogen-bond basicity, electron lone pair interactions, and changes in cohesion. The changes in system constants as a function of temperature and composition are simply modeled as smooth quadratic response surfaces. Curvature in the response surfaces along the composition axis is significant while changes along the temperature axis are modest for both stationary phase types. Cluster analysis is used to demonstrate that the mixed poly(dimethylsiloxane)/poly(ethylene glycol) stationary phases containing 0.5 and 0.85 weight fraction of poly(ethylene glycol) have different selectivity to a database of common open-tubular column stationary phases. The mixed poly(dimethylsiloxane)/poly(ethylene glycol) stationary phase containing 0.10 weight fraction of poly(ethylene glycol) has similar selectivity to the poly(cyanopropylphenyldimethylsiloxane) containing 6% cyanopropylphenyl monomer groups, and could replace the mixed phase for all but the most critical of separations.
Co-reporter:Claire Lepont, Ajith D. Gunatillaka and Colin F. Poole
Analyst 2001 vol. 126(Issue 8) pp:1318-1325
Publication Date(Web):11 Jul 2001
DOI:10.1039/B102719K
The solvation parameter model is used to study the retention mechanism of neutral organic compounds on porous graphitic carbon with methanol–water mobile phases containing from 0–100% (v/v) methanol. The dominant contribution to retention is the cavity formation–dispersion interaction term, composed of favorable interactions in the mobile phase (hydrophobic effect) and additional contributions from adsorption on the graphite surface. Electron lone pair and dipole-type interactions in the adsorbed state result in increased retention. Hydrogen-bonding interactions are more favorable in the mobile phase resulting in lower retention. The changes in the system constants of the solvation parameter model for cavity formation–dispersion interactions and hydrogen-bond interactions are linearly related to the volume fraction of water in the mobile phase. The system constants for electron lone pair interactions and dipole-type interactions are non-linear and go
through a maximum and minimum value, respectively, at a specific mobile phase composition. The solvation parameter model poorly predicts the retention properties of angular molecules. This is probably due to the failure of the characteristic volume to correctly model the contact surface area for the interaction of angular molecules with the planar graphite surface. General factors affecting the quality of model fits for adsorbents are discussed.
Co-reporter:Colin F Poole, Qinglin Li, Waruna Kiridena, Wladyslaw W Koziol
Journal of Chromatography A 2001 Volume 912(Issue 1) pp:107-117
Publication Date(Web):30 March 2001
DOI:10.1016/S0021-9673(01)00560-X
The solvation parameter model is used to study the influence of temperature and composition on the selectivity of nine poly(siloxane) and two poly(ethylene glycol) stationary phase chemistries for open-tubular column gas chromatography. A database of system constants for the temperature range 60–140°C was constructed from literature values with additional results determined for HP-50+, DB-210, DB-1701, DB-225 and SP-2340 columns. The general contribution of monomer composition (methyl, phenyl, cyanopropyl, and trifluoropropyl substituents) on the capacity of poly(siloxane) stationary phases for dispersion, electron lone pair, dipole-type and hydrogen-bond interactions is described. The selectivity coverage of the open-tubular column stationary phases is compared with a larger database for packed column stationary phases at a reference temperature of 120°C. The open-tubular column stationary phases provide reasonable coverage of the range of dipole-type and hydrogen-bond base interactions for non-ionic packed column stationary phases. Deficiencies are noted in the coverage of electron lone pair interactions. None of the open-tubular column stationary phases are hydrogen-bond acids. The system constants are shown to change approximately linearly with temperature over the range 60–140°C. The intercepts and slopes of these plots are used to discuss the influence of temperature on stationary phase selectivity.
Co-reporter:Waruna Kiridena, Wladyslaw W Koziol, Colin F Poole
Journal of Chromatography A 2001 Volume 932(1–2) pp:171-177
Publication Date(Web):12 October 2001
DOI:10.1016/S0021-9673(01)01236-5
The solvation parameter model is used to study the influence of composition and temperature on the selectivity of two poly(siloxane) stationary phases used for open-tubular capillary column gas chromatography. The poly(methyltrifluoropropyldimethylsiloxane) stationary phase, DB-200, has low cohesion, intermediate dipolarity/polarizability, low hydrogen-bond basicity, no hydrogen-bond acidity, and repulsive electron lone pair interactions. The DB-VRX stationary phase has low cohesion, low dipolarity/polarizability, low hydrogen-bond basicity and no hydrogen-bond acidity and no capacity for electron lone pair interactions. The selectivity of the two stationary phases is complementary to those in a database of 11 stationary phase chemistries determined under the same experimental conditions.
Co-reporter:Qinglin Li
Journal of Separation Science 2001 Volume 24(Issue 2) pp:129-135
Publication Date(Web):20 FEB 2001
DOI:10.1002/1615-9314(20010201)24:2<129::AID-JSSC129>3.0.CO;2-L
The solvation parameter model is used to study selectivity differences among five open tubular columns from different sources coated with an immobilized poly(dimethyldiphenylsiloxane) stationary phase containing 5% diphenylsiloxane monomer groups. By regression analysis of the system constants and retention factors it is demonstrated that all five columns possess similar selectivity with minor differences in their hydrogen-bond basicity over the temperature range 60 to 140°C. Differences in selectivity between an arylene-siloxane copolymer with separation properties similar to the poly(dimethyldiphenylsiloxane) stationary phase are somewhat larger, with the copolymer stationary phase being less cohesive and more hydrogen-bond basic than the poly(dimethyldiphenylsiloxane) stationary phases. A performance-deteriorated poly(dimethyldiphenylsiloxane) stationary phase is shown to be less cohesive, more hydrogen-bond basic and dipolar/polarizable than a performance-acceptable column. The selectivity differences between the performance-acceptable and performance-deteriorated stationary phase are much larger than the difference between columns of a generic type.
Co-reporter:Colin F. Poole, Qinglin Li, Waruna Kiridena, Wladyslaw W. Koziol
Journal of Chromatography A 2000 Volume 898(Issue 2) pp:211-226
Publication Date(Web):17 November 2000
DOI:10.1016/S0021-9673(00)00829-3
The solvation parameter model is used to study differences in selectivity for poly(ethylene glycol) stationary phases for packed column (Carbowax 20M) and fused-silica, open-tubular column (HP-20M, AT-Wax, HP-INNOWax and DB-FFAP) gas chromatography. All phases are dipolar, strongly hydrogen-bond basic with no hydrogen-bond acidity and of moderate cohesion. No two phases are exactly alike, however, and selectivity differences identified with cavity formation and dispersion interactions, n- and π-electron pair interactions, dipole-type interactions and hydrogen-bond interactions are quantified by differences in the system constants at a fixed temperature where retention occurs solely by gas–liquid partitioning. The system constants vary linearly with temperature over the range 60–140°C (except for n- and π-electron pair interactions which are temperature invariant) facilitating a general comparison of the importance of temperature on selectivity differences for compared phases. From a mechanistic point of view it is demonstrated that selectivity differences can result from chemical differences between the poly(ethylene glycol) stationary phases and from differences in the relative contribution of interfacial adsorption to the retention mechanism. The latter depends on both system properties and solute characteristics.
Co-reporter:Ajith D. Gunatilleka and Colin F. Poole
Analyst 2000 vol. 125(Issue 1) pp:127-132
Publication Date(Web):26 Jan 2000
DOI:10.1039/A907235G
The solvation parameter model is used to construct equations
for the estimation of the non-specific toxicity of neutral organic
compounds to five organisms used for short-term toxicity testing. For the
bacteria Vibrio fischeri (MicrotoxTM test) and
Pseudomonas putida, the protozoan Tetrahymena pyriformis
(Tetratox test), the green alga Scendesmus quadricauda and
the brine shrimp Artemia salina, the main factors resulting in
increased non-specific toxicity are size (dominantly) and lone-pair
electron interactions, with hydrogen-bond basicity the most important
solute property reducing toxicity. Species differences in relative
non-specific toxicity are largely related to differences in cohesion and
hydrogen-bond acidity of the biomembranes. The models for non-specific
toxicity are proposed as an alternative to the octanol–water
distribution constant for the determination of baseline toxicity. Failure
of the octanol–water distribution constant to model non-specific
toxicity is quantitatively explained by its inability to adequately
characterize the sorption properties of the biomembranes for compounds with
varied properties.
Co-reporter:Waruna Kiridena;Wladyslaw W. Koziol;Qinglin Li
Journal of Separation Science 2000 Volume 23(Issue 10) pp:603-608
Publication Date(Web):27 SEP 2000
DOI:10.1002/1521-4168(20001001)23:10<603::AID-JHRC603>3.0.CO;2-W
Co-reporter:Sanka N. Atapattu and Colin F. Poole
Environmental Science: Nano 2009 - vol. 11(Issue 4) pp:NaN822-822
Publication Date(Web):2009/01/29
DOI:10.1039/B818063F
The solvation parameter model is used to characterize interactions responsible for the sorption of varied organic compounds by diesel soot and atmospheric aerosols at 15 °C and 50% relative humidity. Individual models are obtained for eight aerosol samples characterized as urban, suburban, rural and coastal. Combining the individual aerosol models resulted in a general aerosol model with only a minor loss of modeling power for alkanecarboxylic acids and low-molecular weight alcohols compared with the individual models. A second group of compounds identified as weak nitrogen-containing bases were consistent outliers to all models most likely due to participation in ion-exchange interactions not considered by the models. The diesel soot and atmospheric aerosols exhibit similar characteristics with respect to their sorption interactions although differences in relative magnitude allow the two particle types to be easily distinguished. Sorption interactions are favored by strong dispersion interactions for both particle types. Of note is the strong hydrogen-bond basicity and relatively weak hydrogen-bond acidity of these materials. The particles are quite dipolar/polarizable and slightly electron lone pair repulsive. The sorption properties of the atmospheric aerosols are influenced by the relative humidity, in particular, the aerosols become significantly more hydrogen-bond acidic at high relative humidity most likely due to incorporation of increasing amounts of condensed or film water in the aerosol phase. Dividing the data into training and test sets suggests that the proposed models are capable of estimating distribution constants (log K) to about 0.20 log units for diesel soot (n = 84) and 0.14 log units for the general atmospheric aerosol model (n = 385) where n indicates the number of compounds included in the model.
![[1,1'-Biphenyl]aceticacid](http://img.cochemist.com/ccimg/51400/51317-25-0.png)
![[1,1'-Biphenyl]aceticacid](http://img.cochemist.com/ccimg/51400/51317-25-0_b.png)
