This work presents the separation performance of a 3D graphene-based porous carbon material (GPCM) as a new stationary phase for capillary gas chromatography (GC). The statically coated GPCM column showed a column efficiency of 3210 plates per m and weak polar nature. Its resolving capability and retention behaviours were investigated by using structural and positional isomers and a complex mixture covering analytes of diverse types. The GPCM column exhibits high resolution for nonpolar to polar isomers and analytes of wide ranging variety. It also displays a different retention mechanism from the commercial polysiloxane column, showing preferential retention of alcohols, aromatics and halogenated compounds. In addition, the GPCM column exhibited good column repeatability and reproducibility with RSD values on retention times in the range of 0.01–0.03% for intra-day, 0.06–0.36% for inter-day and 0.44–2.1% for between-column, respectively. The advantageous separation performance shows the good potential of the GPCM stationary phase for GC analysis.

•Seaweed-like graphitic carbon nitride nanofibers (NF-C3N4) as GC stationary phase.•High selectivity and resolving capability for aliphatic and aromatic isomers.•Advantageous separation performance over the bulk graphitic carbon nitride (g-C3N4).•Good potential for the determination of isomer impurities in real samples.Seaweed-like graphitic carbon nitride (g-C3N4) has a unique porous architecture composed of interlocking g-C3N4 nanofibers (NF-C3N4) with much higher surface area than bulk g-C3N4 and shows good potential in separation science. This work investigated the separation performance of NF-C3N4 as stationary phase for capillary gas chromatographic (GC) separations. The NF-C3N4 column exhibits weak polarity and high column efficiency of 4728 plates/m for n-dodecane. Importantly, it displays good separation performance for a wide range of analytes and shows different retention behaviors from the bulk g-C3N4 column and commercial HP-5MS column with 5% phenylpolysiloxane. Particularly, it shows high resolving capability for both aliphatic and aromatic isomers. In addition, NF-C3N4 column has high thermal stability up to 280 °C and good separation repeatability with relative standard deviation (RSD) values in the range of 0.29–0.61% for intra-day, 0.56–1.1% for inter-day and 2.0–4.9% for between-column, respectively. Moreover, it was applied for the determination of isomer impurities in real samples, showing good potential in GC applications.

•Star-shaped oligothiophene-functionalized truxene stationary phases.•High resolving capability for structural and positional isomers.•Good potential for GC analysis of isomer impurities in real samples.This work reports oligothiophene-functionalized truxene-based stationary phases (TTT, TDT and TFT) with a unique star-shaped π-conjugated architecture for gas chromatographic (GC) separations. They exhibited medium polarity and column efficiency of 3340–3760 plates/m determined by naphthalene at 120 °C. Among them, the TTT stationary phase displayed advantageous resolving capability over the TDT and TFT phases for a wide ranging analytes from apolar to polar, particularly for structural and positional isomers, including alcohols, phenols, halogenated and alkylated benzenes and naphthalenes. Moreover, the TTT column exhibited good thermal stability and repeatability with relative standard deviation (RSD) values of 0.02%–0.07% for run-to-run, 0.10%–0.53% for day-to-day and 2.1%–2.9% for column-to-column, respectively. In addition, it was applied for the determination of isomer impurities in real samples, proving its good potential for practical GC analysis.

•Permethylpillar[5]arene as GC stationary phase.•High-resolution capability for structural and positional isomers.•Good potential for practical use in GC analysis.This work presents the investigation of permethyl pillar[5]arene (MP5) as stationary phase for capillary gas chromatographic (GC) separations. The MP5 capillary column fabricated by the sol-gel coating method exhibited weak polarity and high column efficiency over 4200 plates/m for n-dodecane, n-octanol and naphthalene. Particularly, the MP5 stationary phase displays unique retention for dibromoalkanes, which was found to be closely related with the linker length, and shows high resolving capability for a wide range of positional and structural isomers, including alkylbenzenes, chlorobenzenes and chloronitrobenzenes, naphthalene derivatives, phenols and anilines. Moreover, the MP5 column showed good thermal stability and repeatability and reproducibility with the relative standard deviation in the range of 0.02–0.04% for intra-day, 0.32–0.46% for inter-day and 1.5–3.4% for between-column, respectively. This work demonstrates an promising future of pillar[n]arenes as a new type of stationary phase in chromatographic separations.

•π-Extended triptycene-based stationary phase integrated by 2D and 3D units.•High-resolution capability for structural and positional isomers.•Good potential for determination of isomer impurities in real samples.Triptycene-based materials feature favorable physicochemical properties and unique molecular recognition ability that offer good potential as stationary phases for capillary gas chromatography (GC). Herein, we report the investigation of utilizing a π-extended triptycene material (denoted as TQPP) for GC separations. As a result, the TQPP capillary column exhibited high column efficiency of 4030 plates m−1 and high-resolution performance for a wide range of analytes, especially structural and positional isomers. Interestingly, the TQPP stationary phase showed unique shape selectivity for alkanes isomers and preferential retention for analytes with halogen atoms and H-bonding nature mainly through their halogen-bonding and H-bonding interactions. In addition, the TQPP column had good repeatability and reproducibility with the RSD values of 0.02–0.34% for run-to-run, 0.09–0.80% for day-to-day and 1.4–5.2% for column-to-column, respectively, and favorable thermal stability up to 280 °C. This work demonstrates the promising future of triptycene-based materials as a new class of stationary phases for GC separations.Download high-res image (94KB)Download full-size image

This work explored the separation performance of two new dithienyl benzothiadiazole (TBT)-based materials, namely 4,7-di(5-allyl-2-thienyl)benzothiadiazole (TBT-AA) and 4-(5-allyl-2-thienyl)-7-(5-dodecyl-2-thienyl)benzothiadiazole (TBT-AC12), as the stationary phases for capillary gas chromatography (GC). The TBT-AA and TBT-AC12 columns exhibited medium polarity and achieved a column efficiency of 3700 plates per m and 3800 plates per m, respectively, by n-dodecane under 100 °C. They showed high-resolution performance for analytes of different varieties and advantageous resolving capability for positional and structural isomers, such as chloronitrobenzenes, dibromobenzenes, cymenes and hexanes, over the polysiloxane stationary phase with similar polarity. Moreover, the TBT-based stationary phases display different retention behaviours from the conventional phase via diversified molecular interactions covering π–π and π–π EDA, halogen-bonding, H-bonding interactions and van der Waals forces. Also, they exhibited good column repeatability with the relative standard deviation (RSD) values of less than 0.12% for run-to-run, 1.8% for day-to-day and 5.0% for column-to-column, respectively. This work demonstrates the good potential of the TBT-based stationary phases for GC separations.

This work describes the separation performance of the thiophene-functionalized truxene dendrimer (TFTD) as the stationary phase for gas chromatography (GC). An investigation was performed regarding its polarity, column efficiency, separation performance, column repeatability, reproducibility and thermal stability. As a result, the TFTD column showed a high column efficiency of 4420 plates m−1, and weak polarity on the basis of its McReynolds constants. It exhibited high resolving capability for a wide range of analytes, particularly for phenols, anilines, alkylated and halogenated benzenes, showing distinct advantages over the TFT and commercial columns. Moreover, the TFTD column displayed good column repeatability and reproducibility with RSD values in the range of 0.02–0.19% for intra-day, 0.72–1.7% for inter-day and 1.3–4.9% for between-column, respectively. The present work demonstrates the promising future of π-conjugated thiophene-functionalized dendrimers in separation science.

•Unique amphiphilic selectivity for apolar to polar analytes.•High-resolution capability for structural and positional isomers.•Good column inertness for analytes prone to peak tailing.Dicyanuric-functionalized polycaprolactone (DPCL) was explored for its separation performance in gas chromatography (GC). The statically coated DPCL capillary column (0.25 mm, i.d.) showed column efficiency of 3460 plates/m determined by naphthalene at 120 °C. McReynolds constants and Abrahaḿs system constants were also determined to evaluate the polarity and possible molecular interactions of the stationary phase. As a result, DPCL column exhibited excellent separation performance for diverse types of analytes with good peak shapes. Most interestingly, it shows unique amphiphilic selectivity and high-resolution capability for both apolar to polar isomers. In addition, DPCL column had good column repeatability with the RSD values below 0.06% for run-to-run, 0.09–0.40% for day-to-day and 1.7–3.6% for column-to-column, and good thermal stability up to 280 °C. The high selectivity and resolving capability demonstrate the great advantages of the DPCL stationary phase for simultaneous determination of analytes of great variety in complex samples.

•Preferential retention for aromatic and H-bonding analytes.•Unique ordered conjugated structure with high in-plane nitrogen content.•High resolving ability for alkane and aromatic isomers.This work presents the first example of utilization of graphitic carbon nitride (g-C3N4) as stationary phase for capillary gas chromatographic (GC) separations. The statically coated g-C3N4 column showed the column efficiencies of 3760 plates/m and weak polarity. Its resolving capability and retention behaviours were investigated by using the Grob test mixture, and mixtures of diverse types of analytes, and structural and positional isomers. The results showed superior separation performance of the g-C3N4 stationary phase for some critical analytes and preferential retention for aromatic analytes. Specifically, it exhibited high-resolution capability for aromatic and aliphatic isomers such as methylnaphthalenes and dimethylnaphthalenes, phenanthrene and anthracene and alkane isomers. In addition, g-C3N4 column showed excellent thermal stability up to 280 °C and good repeatability with relative standard deviation (RSD) values less than 0.09% for intra-day, below 0.23% for inter-day and in the range of 1.9–8.4% for between-column, respectively. The advantageous separation performance shows the potential of g-C3N4 and related materials as stationary phase in GC and other separation technologies.

•Preferential retention of the iptycene phase for H-bonding and aromatic analytes.•Unique retention behaviors originating from its 3D rigid aromatic structure.•High resolving ability for positional isomers.Unique structures and molecular recognition ability endow iptycene derivatives with great potential as stationary phases in chromatography, which, however, has not been explored yet. Herein, we report the first example of utilizing a pentiptycene quinone (PQ) for gas chromatographic (GC) separations. Remarkably, the statically coated capillary column with the stationary phase achieved extremely high column efficiency of 4800 plates/m. It exhibited preferential retention and high resolving capability for H-bonding and aromatic analytes and positional isomers, showing advantages over the ordinary polysiloxane phase. Moreover, the fabricated iptycene column showed excellent separation repeatability with RSD values of 0.02–0.06% for intra-day, 0.20–0.35% for inter-day and 3.1-5.5% for between-column, respectively. In conclusion, iptycene derivatives as a new class of stationary phases show promising future for their use in GC separations.

•High resolving ability for xylene isomers and di- and tri-PCB isomers.•Retention for the PCBs related with their dihedral angles.•High column thermal stability and excellent repeatability.Herein we report the first example of exploring truxene-based derivatives for gas chromatographic (GC) separations. The fabricated thiophene-functionalized truxene (TFT) column exhibited weak polarity and efficiencies as high as 4000 plates/m for 0.250 mm i.d. columns. TFT column showed preferential retention for halogenated and alkyl benzene analytes, and especially, high resolving capability for the xylene isomers, di- and trichlorobiphenyls (di-CB and tri-CB) isomers. Interestingly, its unique retentions for the latter analytes were found to be closely related with their dihedral angles and the locations of chlorine atoms. This finding on the retention trend has not been reported in GC separations, which may provide a new perspective in elucidating retention behaviours for specific analytes. Moreover, TFT column exhibited high thermal stability up to 320 °C and excellent repeatability. This work demonstrates the promising future of truxene derivatives in the separation science.

Polydopamine (PDA) coating, a nature-inspired polymer, has attracted great attention in many areas due to its high adhesion strength and stability on almost all types of substrate surfaces. This work presents the first example of using PDA coating as a column pretreatment method in capillary gas chromatography (GC) and its employment in the column fabrication of cucurbit[7]uril (CB7) stationary phase. The fabricated PDA-CB7 column exhibited weakly polar nature and had advantages over CB7 column without PDA for the separations of some critical analytes in GC. This work demonstrates the advantage and potential of using PDA as a facile column pretreatment method in capillary GC column fabrication.This work presents the first report on using polydopamine coating as a facile column pretreatment method in the column fabrication for capillary gas chromatography.

•Preferential retention of CTV for aromatic and halogenated compounds.•High resolving ability for structural isomers.•Different retention behaviors from the conventional stationary phase.•Good repeatability in separation.Cyclotriveratrylene (CTV) is reported here for the first time as stationary phase for capillary gas chromatographic (GC) separations. CTV stationary phase showed weak polarity comparable to the conventional 5% phenyl polysiloxane stationary phase but exhibited different retention behaviours and higher resolution for some of the indicated analytes. Most importantly, CTV stationary phase exhibited preferential selectivity for halogenated compounds, positional and geometrical isomers. Effect of column temperature on retention and thermal stability of CTV column were also investigated. Moreover, CTV capillary column showed good repeatability in terms of run-to-run, day-to-day and column-to-column. The unique physicochemical features and efficient separation ability for analytes of close properties show the potential of CTV as a new-type stationary phase in GC as well as separation science.

This work presents a facile strategy by integrating cucurbit[7]uril (CB7) with a guanidinium-based ionic liquid (GBIL) into a binary stationary phase for gas chromatographic separations. A CB7-IL capillary column was statically fabricated with high column efficiency of 4360 plates per m. McReynolds constants and Abraham solvation system constants were utilized to characterize the polarity and solvation properties of this new binary phase. Its selectivity and resolving ability were investigated by separation of analytes of different types, showing advantages over the neat CB7 and GBIL columns possible due to their synergistic effect. Moreover, the CB7-IL column showed good repeatability and thermal stability. The RSD values of the analytes are in the range of 0.01–0.10% for intra-day, 0.06–0.23% for inter-day and 1.5–4.7% for between-column, respectively. The proposed strategy takes full advantages of CB7 and GBIL in selectivity and separation performance and shows potential in separation science.

This work investigated the selectivity of guanidinium-based ionic liquid (GBIL), namely N,N,N′,N′-tetramethyl-N′′,N′′-dioctylguanidinium bis(trifluoromethylsulfonyl)imide (DOTMG-NTf2), in gas chromatographic (GC) separations on the basis of our previous work. The fabricated GBIL capillary column exhibited column efficiency of 4320 plates per m and its selectivity and retention behaviours were explored with various samples including the mixtures of 15 analytes of diverse types, and structural and positional isomers. In this work, we found the intrinsic amphiphilic selectivity of the GBIL phase for nonpolar and polar analytes, showing advantages over the conventional polar phase for GC separation of analytes of a wide range of polarity. Most interestingly, it exhibits unique prolonged retention for linear alkanes, which has not been reported for polar stationary phases. Also, this work presents a new perspective regarding the retention behaviours of GC stationary phases.

This work reports the first example of employing bio-inspired polydopamine (PDA) in capillary column fabrication of a graphene stationary phase (denoted as G-PDA@capillary) for gas chromatographic (GC) separations. The as-fabricated G-PDA@capillary column achieved improved column efficiency of 3400 plates per m and separation performance in contrast to the graphene column without PDA (G@capillary). In particular, it exhibited high selectivity and resolving ability for alkane isomers, alcohol isomers, substituted benzenes with diverse groups and many other types of analytes. Additionally, the G-PDA@capillary column showed good repeatability with RSD values less than 0.02% for run-to-run, 0.16% for day-to-day and 5.0% for column-to-column, respectively, and thermal stability up to 300 °C. This work demonstrates the feasibility of the proposed strategy by integrating graphene sheets with PDA coating, which is efficient in addressing the current problem with graphene sheets and exploring its full potential in GC separations.

Graphene oxide (GO) has attracted extensive attention due to its unique properties and potential applications. Here, we report the investigation of GO nanosheets as a stationary phase for capillary gas chromatographic (GC) separations. The GO column, fabricated by a new one-step coating approach, showed average McReynolds constants of 308, suggesting the medium polar nature of the GC stationary phase. The GO stationary phase achieves good separation for analytes of different types with good peak shapes, especially for H-bonding analytes, such as alcohols and amines. The different retention behaviors of GO stationary phase from the conventional stationary phase may originate from its multiple interactions with analytes, involving H-bonding, dipole–dipole, π–π stacking and dispersive interactions. Moreover, GO column showed good separation reproducibility with relative standard deviation (RSD%) less than 0.24% (n = 5) on retention times of analytes.This work presents the investigation of graphene oxide nanosheets as a stationary phase for capillary gas chromatography.

•High resolving ability of CB7-SG stationary phase for capillary GC separations.•Different retention behaviors from the conventional stationary phase.•Good thermal stability.Here we report the separation performance of a new stationary phase of cucurbit[7]uril (CB7) incorporated into an ionic liquid-based sol-gel coating (CB7-SG) for capillary gas chromatography (GC). The CB7-SG stationary phase showed an average polarity of 455, suggesting its polar nature. Abraham system constants revealed that its major interactions with analytes include H-bond basicity (a), dipole–dipole (s) and dispersive (l) interactions. The CB7-SG stationary phase achieved baseline separation for a wide range of analytes with symmetrical peak shapes and showed advantages over the conventional polar stationary phase that failed to resolve some critical analytes. Also, it exhibited different retention behaviors from the conventional stationary phase in terms of retention times and elution order. Most interestingly, in contrast to the conventional polar phase, the CB7-SG stationary phase exhibited longer retentions for analytes of lower polarity but relatively comparable retentions for polar analytes such as alcohols and phenols. The high resolving ability and unique retention behaviors of the CB7-SG stationary phase may stem from the comprehensive interactions of the aforementioned interactions and shape selectivity. Moreover, the CB7-SG column showed good peak shapes for analytes prone to peak tailing, good thermal stability up to 280 °C and separation repeatability with RSD values in the range of 0.01–0.11% for intra-day, 0.04–0.41% for inter-day and 2.5–6.0% for column-to-column, respectively. As demonstrated, the proposed coating method can simultaneously address the solubility problem with CBs for the intended purpose and achieve outstanding GC separation performance.

•Calix[4]pyrroles as new GC stationary phases are presented.•Calix[4]pyrroles show highly selective separation performance.•Calix[4]pyrroles have a great potential for practical applications.Calix[4]pyrroles offer a great potential as stationary phases for gas chromatography (GC) due to their unique structures and physicochemical properties. Herein we present the first report of using two calix[4]pyrroles, namely meso-tetra-cyclohexylcalix[4]pyrrole (THCP) and meso-octamethylcalix[4]pyrrole (OMCP). These stationary phases were statically coated onto capillary columns and investigated in terms of column efficiency, polarity, separation performance, thermal stability and repeatability. The columns achieved column efficiencies of 2200–3000 plates/m and exhibited nonpolar nature with an average polarity of 67 for THCP and 64 for OMCP, respectively. THCP stationary phase shows high selectivity for analytes of different polarity and exhibits nice peak shapes, especially for aldehydes, alcohols and anilines that are prone to severe peak tailing in GC analysis. Interestingly, THCP stationary phase possesses superior resolving ability for aniline and benzenediol positional isomers while OMCP shows preferential selectivity for nonpolar analytes such as hexane isomers. Moreover, calix[4]pyrrole columns also have good thermal stability up to 260 °C and repeatability with a relative standard deviation (RSD%) of less than 0.10% for run-to-run and less than 5.2% for column-to-column. This work demonstrates the unique separation performance of calix[4]pyrroles and their promising future as a new class of GC stationary phases.

•Cucurbit[n]urils as new stationary phases for capillary GC.•High selectivity for analytes of different variety.•Good perspectives in thermal stability.•Great potential in analytical practice.Cucurbit[n]urils (CBs) possess unique structures and physicochemical properties as well as excellent thermal stability. These characteristics concur to make them good candidates for stationary phases in capillary gas chromatographic (GC) separations. Herein, CB7 and CB8 in neat (CB7, CB8) and binary (CB7–CB8) forms were investigated for this purpose. After they were statically coated onto fused silica capillary columns, the CB columns were evaluated in terms of chromatographic parameters, separation performance, thermal stability and column repeatability. The columns had efficiencies ranging from 1060 to 2200 plates per meter determined by n-dodecane at 100 °C and exhibited nonpolar to weakly polar nature. These CBs columns showed good separation performance for a wide range of analytes such as n-alkanes, aromatic hydrocarbons, esters, aldehydes, ketones, alcohols and the Grob mixture, and exhibited nice peak shapes for analytes that are liable to peak-tailing in GC analysis. The results also proved the good column repeatability and thermal stability of the CB columns. No noticeable decreases in both retention times and resolution or appreciable baseline drift were observed after the columns were conditioned up to 250 °C (CB8 and CB7–CB8 columns) or 280 °C (CB7 column). This work demonstrates the promising future of CBs as a new class of GC stationary phase. To the best of our knowledge, this is the first report on using CB stationary phases in capillary GC separations.

•New stationary phase for GC separation.•High selectivity for analytes of different variety.•Good thermal stability of CB6-GBIL column.•Great potential in practical application.Cucurbit[n]urils (CBs) possess unique structures and selective interactions with analytes of different variety and high thermal stability and show a great potential as stationary phases for capillary gas chromatography (GC). This work presents the first description of CB6 in combination with a new guanidinium-based ionic liquid (GBIL) as the GC stationary phase by using sol–gel coating method for the preparation of the CB6-GBIL and GBIL columns. Introduction of GBIL greatly improved the solubility of CB6 in the sol solution and successfully made the use of CBs for the intended purpose feasible. The CB6-GBIL and GBIL columns had average polarity of 179 and 280, respectively, suggesting their medium polar nature. The CB6-GBIL column achieves good resolution for a wide range of analytes and exhibits different retention behaviors and resolution for some of the analytes from the GBIL column and the commercial column. Moreover, it also shows good thermal stability up to 250 °C. The proposed method integrates the full advantages of CBs, ionic liquids and sol–gel coating method and provides an efficient and feasible way for the wider application of CBs in separation science.

Room temperature ionic liquids (RTILs) as stationary phases for gas chromatography (GC) have made great achievements in both research and applications over the last decades. Until now, all of the RTIL stationary phases reported have involved imidazolium, ammonium, pyrrolidinium, and phosphonium-based RTILs, and however, no publications are available using guanidinium-based ionic liquids (GBILs) as GC stationary phases except two preliminary reports from our group. In the present work, three hexaalkyl GBILs stationary phases, namely N, N,N′,N′-tetramethyl-N″, N″-dioctylguanidinum hexafluophosphate (DOTMG-PF6), N,N,N′,N′-tetramethyl-N″, N″-dioctylguanidinium bis (trifluoromethylsulfonyl) imide (DOTMG-NTf2), and N,N,N′,N′-tetraoctyl-N″, N″-dimethylguanidinium bis (trifluoromethylsulfonyl) imide (TODMG-NTf2), were synthesized and used as stationary phases for GC separation after they were statically coated onto the inner walls of fused-silica capillary columns. The evaluation of DOTMG-PF6 and TODMG-NTf2 as GC stationary phases is reported here for the first time, whereas additional results on the DOTMG-NTf2 stationary phase are added here on the basis of our previous report. In this work, McReynolds constants and Abraham solvation system constants are used to evaluate the average polarity and the solvation properties of the GBILs stationary phases for GC separation, respectively. The results show that the GBILs stationary phases exhibit medium polarity with an average polarity of 293–390, and that the major molecular interactions of the GBILs with analytes are dipole/polarizable interactions, H-bond basicity and dispersion forces, etc. After this, the separation performance and thermal stability of the GBILs stationary phases were evaluated, showing that these stationary phases achieve excellent separation for analytes of great variety covering hydrocarbons, alcohols, esters, aldehydes, ketones, amines, amides and aromatics, and exhibit different retention behaviors from the most widely used GC stationary phases such as polyethylene glycol (PEG-20M) and 5% phenyl–95% dimethylpolysiloxane (SE-54) in terms of resolution and elution order, and good thermal stability (at least up to 250 °C). The present work demonstrates that the GBILs stationary phases possess excellent separation performance and thermal stability, and may be applicable as a new type of GC stationary phases for separation of complex samples.Highlights► Guanidinium-based ionic liquids (GBILs) are presented as new GC stationary phases. ► GBILs show excellent separation performance and thermal stability. ► GBILs have different retention behaviors from the widely used stationary phases. ► GBILs can be used for separation of analytes of various nature.

•TBTs as new GC stationary phases are presented.•TBTs show excellent separation performance and thermal stability.•TBTs have a great potential as new separation media for wide applications.Dithienyl benzothiadiazole (TBT) derivatives are characteristic of specific molecular structures and excellent thermal stability, offering the great potential for their use as stationary phases for capillary gas chromatography (GC). However, no related publications are available to date. Here we first report the exploration of two TBT derivatives, namely, 4,7-bis(5-dodecylthiophen-2-yl) benzothiadiazole (TBT-C12, a new derivative), and 4,7-di(thiophen-2-yl) benzothiadiazole (TBT), for the purpose. First, TBT-C12 and TBT were synthesized and statically coated onto capillary columns. Both of the as-prepared columns were characterized as nonpolar nature by the determined McReynolds constants. The results showed that both TBT-C12 and TBT columns achieved excellent separations for n-alkanes, esters and polycyclic aromatic hydrocarbons (PAHs), and the TBT-C12 column exhibited better thermal stability (up to 280 °C) than the TBT column. Moreover, a comparative study between the TBT-type columns and a commercial column was also made, suggesting the better selectivity of the TBT-type stationary phases toward n-alkanes and PAHs than that of the commercial one. Additionally, thermodynamic parameters suggested that the retention behaviors of n-alkanes and PAHs on the TBT-C12 column was mainly controlled by entropy change (ΔS). In conclusion, this work demonstrates the excellent chromatographic performance of TBT derivatives as a new type of GC stationary phases and their potential in separation science.

A rapid headspace single-drop micro-extraction (mix) gas chromatography mass spectrometry (SDME–GC–MS) for the analysis of the volatile compounds in Herba Asari was developed in this study. A mixed solvent of n-tridecane and butyl acetate (1:1) was finally used for the extraction at 70 °C for 15 min with sample amount of 0.750 g and 100 mesh particle size. Under the determined conditions, the pound samples of Herba Asari were directly applied for the analysis. SDME–GC–MS, SPME–GC–MS and SD–GC–MS methods were compared and the results showed that SDME–GC–MS method was a simple, inexpensive and effective way to measure the volatile compounds in Herba Asari and could be used for the analysis of volatile compounds in complex samples.Mixed solvent extraction based on SDME was developed for analysis of volatile components in TCM.

Ionic liquids (ILs) grafted polymethylsiloxane (PMS) stationary phases (IL-PMS) for capillary gas chromatography (CGC) are described. The stationary phases were synthesized by grafting 1-vinyl-3-hexylimidazolium (VHIm) with either NTf2− or PF6− anion to poly(methylhydrosiloxane) (PMS-VHIm-NTf2, PMS-VHIm-PF6) and coated statically onto fused-silica capillary columns. Separation characteristics of the stationary phases involving Abraham solvation parameters, separation ability and thermal stability were investigated. The obtained solvation parameters reveal that both IL-PMS stationary phases exhibited unique intermolecular interactions compared with either ILs or PMS due to the synergistic effect of ILs and PMS chemically combining together. The separation performance of the IL-PMS stationary phases was investigated by a Grob mixture and a complex mixture of 26 compounds of different types. The results show that the present stationary phases exhibit excellent resolution and selectivity for the analytes of interest with narrow and symmetric peak shapes. Thermal stability was also investigated by column bleed profiles with satisfactory results. The satisfactory chromatographic performance and thermal stability of the IL-PMS stationary phases suggest their great potential as a new type of CGC stationary phases.

The present study describes guanidinium-based ionic liquids (GBILs) as stationary phases for capillary gas chromatography (CGC) and to the best of our knowledge, no related reports are available up to now. In this study, a hexaalkylguanidinium ionic liquid (DOTMG-NTf2) was synthesized and coated statically onto capillary columns. Selectivity of the stationary phase was evaluated by separating Grob test mixture, test mixture, alcohols mixture, and fatty acid methyl esters mixture, and thermal stability was investigated as well. The present study demonstrates that GBILs as CGC stationary phases exhibit satisfactory selectivity and thermal stability and have a great potential as new candidates for CGC stationary phases.

One chloride-terminated ionic liquid (CTIL) and two hydroxyl-terminated ionic liquids (HTILs) were synthesized and used as stationary phases for capillary gas chromatography (CGC). Molecular interactions of these stationary phases were evaluated by Abraham solvation parameter model, indicating that the CTIL exhibits remarkably strong H-bond basicity and the HTILs possess both H-bond basicity and acidity. The molecular interactions were further confirmed by separation of a complex mixture consisting of ketones, aldehydes, esters, alcohols and aromatic compounds. It was found that the obtained solvation parameters correlate well with the chromatographic performances of the analytes in terms of elution order and resolution. The well correlated relationship between the solvation parameters and the selectivity of the CTIL and HTILs stationary phases is quite helpful in predicting and understanding the retention behaviors of different types of analytes on these stationary phases.

A guanidinium ionic liquid, N, N, N′, N′-tetrahexyl-N″, N″-dimethylguanidinium bis(trifluoromethane)sulfonylimide (THDMG-NTf2), was synthesized and used as stationary phase for capillary gas chromatography. In comparison with imidazolium ionic liquid stationary phase, the present new stationary phase exhibits quite different selectivity and behaves more like a low polar stationary phase. The guanidinium ionic liquid of THDMG-NTf2 exhibited better separation of Grob test mixture than imidazolium ionic liquid of 1-octyl-3-butylimidazolium bis(trifluoromethane)sulfonylimide (OBIM-NTf2). Solvation parameter model was also used to evaluate the selectivity of THDMG-NTf2. Additionally, essential oil of Magnolia biondii Pamp was analyzed to further evaluate the selectivity of THDMG-NTf2 for a sample of complicated components. Satisfactory separation of the essential oil was achieved on a THDMG-NTf2 column (10 m) while using a commercial column (30 m) as reference. The present study shows that the guanidinium ionic liquid possesses novel chromatographic selectivity and has great potential for wide applications.

A new ionic liquids grafted polysiloxane used as stationary phase for capillary gas chromatography (CGC) is described. The stationary phase of 1-vinyl-3-hexylimidazolium hexafluorophosphate anchored to polysiloxane (PMHS-[VHIm][PF6]) was synthesized, characterized and coated onto capillary columns by static coating. The results show that the present stationary phase exhibits a very good chromatographic resolution and selectivity for Grob test mixture and alcohols with baseline resolution and symmetry peaks. The present work suggests that novel stationary phase has a great potential for further development and application.

A headspace solvent microextraction–gas chromatography–mass spectrometry (HSME–GC–MS) method was described for the analysis of volatile compounds from Curcuma wenyujin Y.H. Chen et C. Ling. A comparison was made between HSME–GC–MS, solid-phase microextraction (SPME)–GC–MS and steam distillation (SD)–GC–MS methods. The number of the identified compounds was 66 for HSME–GC–MS, 71 for SPME–GC–MS and 63 for SD–GC–MS, respectively. HSME–GC–MS was found to share most of the compounds in common with the other two methods. Compared with the other two methods, HSME–GC–MS has a lower cost, more choices of extraction solvents and requires a smaller amount of sample and can directly utilizes the ground powder of traditional Chinese medicines (TCMs) for the analysis. In conclusion, HSME–GC–MS method is a simple, inexpensive and effective method for the analysis of volatile compounds in TCMs.

A solid-phase microextraction coupled with gas chromatography–mass spectrometry (SPME–GC–MS) for analysis of the volatile compounds from Curcuma wenyujin Y.H. Chen et C. Ling is described. SPME parameters (fiber type, extraction temperature and time, headspace volume and desorption time) and GC conditions were tested. The powdered sample of C. wenyujin Y.H. Chen et C. Ling was directly analyzed by SPME–GC–MS and 72 compounds were identified. The results from SPME–GC–MS were compared with those obtained from steam distillation gas chromatography–mass spectrometry (SD-GC–MS) with a good agreement. The results show that SPME–GC–MS method is a fast, simple and efficient way for the analysis of volatile components from traditional Chinese medicines (TCMs).

A liquid chromatographic method is described for the simultaneous determination of cefalexin and trimethoprim in dog plasma. A simple protein precipitation procedure was adopted for the sample preparation with satisfactory extraction recoveries for both analytes. Chromatographic separation of the analytes was achieved on a C18 column using a mixture of 2 mol/l formate buffer (pH 3.5), methanol and acetonitrile (22:7:7, v/v/v) containing a 0.002 mol/l sodium dodecyl sulfate as mobile phase and detection was performed at 240 nm. The linearity was obtained over the concentration ranges of 1.0–100.0 μg/ml for cefalexin and 0.5–50.0 μg/ml for trimethoprim. For each level of QC samples including the lower limit of quantification, both inter- and intra-day precisions (R.S.D.) were ≤14.0% for cefalexin and ≤11.4% for trimethoprim, and accuracy (RE) was −1.4% for cefalexin and −3.0% for trimethoprim. The present LC method was successfully applied to the pharmacokinetic studies of coformulated cefalexin dispersible tablets after oral administration to beagle dogs.

A liquid chromatographic–tandem mass spectrometric method (LC–MS/MS) for the determination of ulifloxacin, the active metabolite of prulifloxacin, in human plasma is described. After sample preparation by protein precipitation with methanol, ulifloxacin and ofloxacin (internal standard) were chromatographically separated on a C18 column using a mobile phase consisting of methanol, water and formic acid (70:30:0.2, v/v/v) at a flow rate of 0.5 ml/min and then were detected using MS/MS by monitoring their precursor-to-product ion transitions, m/z 350 → m/z 248 for ulifloxacin and m/z 362 → m/z 261 for ofloxacin, in selected reaction monitoring (SRM) mode. Positive electrospray ionization was used for the ionization process. The linear range was 0.025–5.0 μg/ml for ulifloxacin with a lower limit of quantitation of 0.025 μg/ml. Within- and between-run precision was less than 6.6 and 7.8%, respectively, and accuracy was within 2.0%. The recovery ranged from 92.1 to 98.2% at the concentrations of 0.025, 0.50 and 5.0 μg/ml. Compared with the reported LC method, the present LC–MS/MS method can directly determine the ulifloxacin in human plasma without any need of derivatization. The present method has been successfully used for the pharmacokinetic studies of a prulifloxacin formulation product after oral administration to healthy volunteers.

A simple and sensitive liquid chromatography–mass spectrometry method is described for the determination of nicardipine in human plasma. Chromatographic separation of the analyte was achieved on a C18 column using a mobile phase of methanol, water and formic acid (320:180:0.4, v/v/v). Selected ion monitoring (SIM) in positive mode was used for analyte quantification at m/z 480.2 for nicardipine and m/z 256.4 for diphenhydramine. The run time was less than 5 min. The linearity over the concentration range of 0.05–20.0 ng/ml for nicardipine was obtained and the lower limit of quantification was 0.05 ng/ml. For each level of QC samples, inter-day and intra-day precisions (R.S.D.) were ≤9.3 and 11.1%, respectively, and accuracy (RE) was ±4.9%. The present LC–MS method was successfully applied in the pharmacokinetic studies of nicardipine hydrochloride delayed-release tablets in two formulations after oral administration to healthy volunteers.

A liquid chromatography–mass spectrometry (LC–MS) method for the determination of roxithromycin in rat lung tissue is described. Liquid–liquid extraction was adopted for sample preparation with recoveries from 72.5 to 76.9% at levels of 0.1, 5.0 and 20.0 μg/ml. Chromatographic separation was performed on a C18 column using a mixture of methanol, water and formic acid (80:20:1, v/v/v) as mobile phase delivered at a flow rate of 0.5 ml/min. Positive selected ion monitoring (SIM) mode was used for the quantification of roxithromycin at m/z 837.7 and clarithromycin (internal standard) at m/z 748.7. The linearity was obtained over the concentration range of 0.05–20.0 μg/ml and the lower limit of quantification was 0.05 μg/ml. For each QC level of roxithromycin, the intra- and inter-day precisions relative standard deviation (R.S.D.) were less than 4.1 and 7.5%, respectively, and accuracy (RE) was ±10.0%. The proposed LC–MS method has been successfully used for the determination of roxithromycin in rat lung tissue after oral administration of roxithromycin formulations to 44 SD rats. The present study demonstrates that the concentration of roxithromycin in rat lung tissues can be significantly increased by ambroxol when they are formulated in combination.

A simple and selective LC method is described for the determination of desloratadine in drug substance and pharmaceutical preparations. Chromatographic separation was achieved on a Diamonsil BDS C18 column using a mobile phase of a mixture of methanol, 0.03 mol/l heptanesulphonic acid sodium and glacial acetic acid (70:30:4, v/v) at a flow rate of 1.0 ml/min with detection at 247 nm. The developed method was validated in terms of selectivity, linearity, limit of quantitation, precision, accuracy and solution stability. The proposed LC method achieved satisfactory resolution between desloratadine and loratadine possibly present in desloratadine drug substance and other impurities in the mother liquor of the synthetic process. It can be used for the synthetic process control and determination of desloratadine in drug substance and pharmaceutical preparations.

A liquid chromatography (LC) method for the determination of ibuprofen in dog plasma is described. Chromatographic separation was performed on a Diamonsil™ C18 column with a C18 guard column using a binary mixture of acetonitrile and 0.02 mol/l phosphate buffer (pH 6.5) (35:65, v/v) delivered at a flow rate of 1.2 ml/min. The linear range for ibuprofen was from 1.0 to 40.0 μg/ml with a limit of quantitation of 1.0 μg/ml. Within-run accuracy and precision ranged from −0.1% to 4.0% and from 1.1% to 5.5% and between-run accuracy and precision ranged from −1.1% to 4.7% and from 1.3% to 7.0%, respectively. The mean extraction recoveries of ibuprofen determined over the concentrations of 1.0, 10.0, and 40.0 μg/ml were (100.5 ± 1.8)%, (99.8 ± 1.0)%, and (99.2 ± 2.3)%. The developed LC method greatly simplified the sample preparation and adopted mild conditions to prevent the possible hydrolysis of the prodrug and was successfully applied to the pharmacokinetic studies of an ibuprofen prodrug in dogs.

A rapid and accurate liquid chromatographic method is described for the simultaneous determination of roxithromycin and ambroxol hydrochloride in a new tablet formulation. Chromatographic separation of the two drugs was achieved on a Diamonsil™ C18 column ( mm, 5 μm). The mobile phase consisting of a mixture of acetonitrile, methanol and 0.5% ammonium acetate (39:11:50 (v/v), pH 5.5) was delivered at a flow rate of 1.0 ml/min. Detection was performed at 220 nm. Linearity, accuracy and precision were found to be acceptable over the concentration range of 201.2–2012.0 μg/ml for roxithromycin and 42.7–427.0 μg/ml for ambroxol hydrochloride, respectively. Separation was complete in less than 10 min. The proposed method can be used for the quality control of formulation products.

An isocratic liquid chromatographic method with UV detection at 210 nm is described for simultaneous determination of amoxicillin sodium and sulbactam sodium in a new combination formulation. Chromatographic separation of the two drugs was achieved on a Hypersil C18 column using a mobile phase consisting of a binary mixture of methanol and 0.01 mol/l sodium acetate (5:95, v/v). The commonly used paired-ion aqueous mobile phase for the determination of penicillins was avoided in this study. The developed LC method offers symmetric peak shape, good resolution and reasonable retention time for both drugs. Linearity, accuracy and precision were found to be acceptable over the concentration ranges of 155.3–1553.0 μg/ml for amoxicillin sodium and 45.0–450.0 μg/ml for sulbactam sodium. The proposed LC method can be used for the quality control of formulated products containing these two drugs.

A rapid, sensitive and accurate liquid chromatographic–tandem mass spectrometric method is described for the determination of tamsulosin in dog plasma. Tamsulosin was extracted from plasma using a mixture of hexane–ethyl acetate (2:1, v/v) and separated on a C18 column interfaced with a triple quadrupole tandem mass spectrometer. The mobile phase consisting of a mixture of methanol, water and formic acid (80:20:1, v/v/v) was delivered at a flow rate of 0.5 ml/min. Atmospheric pressure chemical ionization (APCI) source was operated in positive ion mode. Selected reaction monitoring (SRM) mode using the transitions of m/z 409→m/z 228 and m/z 256→m/z 166.9 were used to quantify tamsulosin and the internal standard, respectively. The linearity was obtained over the concentration range of 0.1–50.0 ng/ml for tamsulosin and the lower limit of quantitation was 0.1 ng/ml. For each level of QC samples, inter- and intra-run precision was less than 5.0 and 4.0% (relative standard deviation (R.S.D.)), respectively, and accuracy was within ±0.3% (relative error (R.E.)). This method was successfully applied to pharmacokinetic study of a tamsulosin formulation product after oral administration to beagle dogs.

A liquid chromatography–mass spectrometry method is described for the determination of tetramethylpyrazine (TMP) and its active metabolite, 2-hydroxymethyl-3,5,6-trimethylpyrazine (HTMP) in dog plasma. This method involves a plasma clean-up step using protein precipitation procedure followed by LC separation and positive electrospray ionization mass spectrometry detection (ESI-MS). Chromatographic separation of the analytes was achieved on a C18 column using a mobile phase of methanol, water and acetic acid (50:50:0.6, v/v/v) at a flow rate of 1.0 ml/min. Selected ion monitoring (SIM) mode was used for analyte quantitation at m/z 137.2 for TMP, m/z 153.2 for HTMP and m/z 195.2 for caffeine. The linearity was obtained over the concentration ranges of 20–6000 ng/ml for TMP and 20–4000 ng/ml for HTMP and the lower limit of quantitation was 20 ng/ml for both analytes. For each level of QC samples, both inter- and intra-day precisions (R.S.D.) were ≤7.4% for TMP and ≤6.0% for HTMP, and accuracy (R.E.) was ±6.0% for TMP and ≤3.5% for HTMP. The proposed LC–MS method was successfully applied to the pharmacokinetic studies of a TMP formulation preparation after oral administration to beagle dogs.

A new isocratic stability indicating HPLC method for determination of tizanidine in drug substance and formulated products is described. Chromatographic separation of tizanidine from the related substances and degraded products was achieved with a Hypersil CN column ( mm, 5 μm) using a mobile phase comprising a mixture of an ion-pairing solution of heptanesulphonic acid sodium salt (HAS), methanol and acetonitrile (50:57:18 (v/v)) within 10 min. The flow-rate was 1.0 ml/min and detection was made at 227 nm. The method has good selectivity towards tizanidine, related substances and degraded products. Limits of quantitation for tizanidine and its synthetic intermediates were determined, ranging from 0.051 to 0.54 μg/ml. The linearity range was found to be 2–20 μg/ml (r=0.9998, n=5). Mean recovery for tizanidine from the tablets was from 99.5 to 99.8%. Precision of the method was 1.0% (n=9). The method can be used for routine analysis and the quality control of tizanidine drug substance and its formulated products.

A simple and accurate HPLC method for determination of oxcarbazepine (OXC) in a new tablet formulation is described. Chromatographic separation was achieved on a Diamonsil C18 column using a mobile phase consisting of acetonitrile, potassium phosphate monobasic buffer (pH 6.8) and water (36:8:56, v/v) at a flow rate of 1.0 ml/min. Absorbance was monitored at 255 nm where OXC has maximum absorption. The linear range of detection for OXC was from 9.96 to 99.6 μg/ml. The proposed method was validated for selectivity, precision, accuracy and limits of detection and quantitation, etc.