Although significant progress has been made in the diagnosis and treatment of colorectal cancer (CRC), it remains a leading cause of cancer death worldwide. Early identification and removal of polyps that may progress to overt CRC is the cornerstone of CRC prevention. Expression of the High Mobility Group A1 (HMGA1) gene is significantly elevated in CRCs as compared with adjacent, nonmalignant tissues. We investigated metabolic aberrations induced by HMGA1 overexpression in small intestinal and colonic epithelium using traveling wave ion mobility mass spectrometry (TWIMMS) in a transgenic model in which murine Hmga1 was misexpressed in colonic epithelium. To determine if these Hmga1-induced metabolic alterations in mice were relevant to human colorectal carcinogenesis, we also investigated tumors from patients with CRC and matched, adjacent, nonmalignant tissues. Multivariate statistical methods and manual comparisons were used to identify metabolites specific to Hmga1 and CRC. Statistical modeling of data revealed distinct metabolic patterns in Hmga1 transgenics and human CRC samples as compared with the control tissues. We discovered that 13 metabolites were specific for Hmga1 in murine intestinal epithelium and also found in human CRC. Several of these metabolites function in fatty acid metabolism and membrane composition. Although further validation is needed, our results suggest that high levels of HMGA1 protein drive metabolic alterations that contribute to CRC pathogenesis through fatty acid synthesis. These metabolites could serve as potential biomarkers or therapeutic targets.Keywords: biomarker discovery; cancer metabolomics ion mobility mass spectrometry; colorectal cancer; HMGA1; ion mobility; mass spectrometry; metabolomics;

The established theory of ion motion within weak electric fields predicts that reduced ion mobility (K0) remains constant as a function of the ratio of electric field strength to drift gas number density (E/N). However, upon increasing the accuracy and precision of K0 value measurements during a previous study, a new relationship was seen in which the K0 values of ions decreased as a function of increasing E/N at field strengths below 4 Td. Here the effect of E/N on the K0 value of an ion has been investigated in order to validate the reality of the phenomenon and determine its cause. The pertinent measurements of voltage and drift time were verified in order to ensure the authenticity of the trend and that it was not a result of a systematic error in parametric measurements. The trend was also replicated on a separate ion mobility spectrometer drift tube in order to further validate its authenticity. As a result, the theory of ion motion within weak electric fields should be revised to reflect the behavior seen here.

Because colorectal cancer (CRC) remains a leading cause of cancer mortality worldwide, more accessible screening tests are urgently needed to identify early stage lesions. We hypothesized that highly sensitive, metabolic profile analysis of stool samples will identify metabolites associated with early stage lesions and could serve as a noninvasive screening test. We therefore applied traveling wave ion mobility mass spectrometry (TWIMMS) coupled with ultraperformance liquid chromatography (UPLC) to investigate metabolic aberrations in stool samples in a transgenic model of premalignant polyposis aberrantly expressing the gene encoding the high mobility group A (Hmga1) chromatin remodeling protein. Here, we report for the first time that the fecal metabolome of Hmga1 mice is distinct from that of control mice and includes metabolites previously identified in human CRC. Significant alterations were observed in fatty acid metabolites and metabolites associated with bile acids (hypoxanthine xanthine, taurine) in Hmga1 mice compared to controls. Surprisingly, a marked increase in the levels of distinctive short, arginine-enriched, tetra-peptide fragments was observed in the transgenic mice. Together these findings suggest that specific metabolites are associated with Hmga1-induced polyposis and abnormal proliferation in intestinal epithelium. Although further studies are needed, these data provide a compelling rationale to develop fecal metabolomic analysis as a noninvasive screening tool to detect early precursor lesions to CRC in humans.Keywords: cancer metabolomics; cancer screening; colorectal cancer; high mobility group A1 (HMGA1) chromatin remodeling protein; ion mobility mass spectrometry;

A high performance liquid chromatograph (HPLC)was interfaced to an atmospheric drift tube ion mobility time of flight mass spectrometry. The power of multidimensional separation was demonstrated using chili pepper extracts. The ambient pressure drift tube ion mobility provided high resolving powers up to 166 for the HPLC eluent. With implementation of Hadamard transform (HT), the duty cycle for the ion mobility drift tube was increased from less than 1% to 50%, and the ion transmission efficiency was improved by over 200 times compared with pulsed mode, improving signal to noise ratio 10 times. HT ion mobility and TOF mass spectrometry provide an additional dimension of separation for complex samples without increasing the analysis time compared with conventional HPLC.

The neuronal metabolomes in rat striatum (STR), prefrontal cortex (PFC), and nucleus accumbens (NAC) were analyzed by Hadamard transform ion mobility mass spectrometry (HT-IMMS) in order to reveal global and specific metabolic changes induced by cocaine self-administration after 1-day or 3-week withdrawal. Metabolite features were comprehensively separated and detected using HPLC-IMMS within minutes. Global metabolic differences were observed by PCA for comparisons between cocaine and saline treatments at 1-day withdrawal time. Metabolite features that were significantly changed were selected using PCA loadings’ plot and unpaired LLL test and then tentatively identified by accurate m/z, yielding a complete profile of metabolic changes induced by cocaine self-administration. The majority of these changes were found at the 1-day withdrawal time, but several of them endured even after 3-week withdrawal from cocaine, and these changes were generally brain region specific. Putatively identified metabolites associated with oxidative stress and energy metabolism were also specifically investigated. We discovered that the dysregulation of creatine/creatinine was different between the STR and NAC, demonstrating that metabolic alterations are brain region specific. Glutathione and adenosine were also changed in their abundance, and the results agreed with previous studies. In general, this study provided a high-throughput analytical platform to perform metabolomics analyses with putative identifications for altered metabolite features induced by cocaine treatment, therefore revealing additional metabolic targets of cocaine-induced changes after early and extended withdrawal times.

Negative ions produced by electrospray ionization were used to evaluate the isomeric heterogeneity of neutral oligosaccharide-alditols isolated from bovine submaxillary mucin (BSM). The oligosaccharide-alditol mixture was preseparated on an off-line high-performance liquid chromatography (HPLC) column, and the structural homogeneity of individual LC fractions was investigated using a Synapt G2 traveling wave ion mobility spectrometer coupled between quadupole and time-of-flight mass spectrometers. Mixtures of isomers separated by both chromatography and ion mobility spectrometry were studied. Tandem mass spectrometry (MS/MS) of multiple mobility peaks having the same mass-to-charge ratio (m/z) demonstrated the presence of different structural isomers and not differences in ion conformations due to charge site location. Although the oligosaccharide-alditol mixture was originally separated by HPLC, multiple ion mobility peaks due to structural isomers were observed for a number of oligosaccharide-alditols from single LC fractions. The collision-induced dissociation cells located in front of and after the ion mobility separation device enabled oligosaccharide precursor or product ions to be separated by ion mobility and independent fragmentation spectra to be acquired for isomeric carbohydrate precursor or product ions. MS/MS spectra so obtained for independent mobility peaks at a single m/z demonstrated the presence of structural variants or stereochemical isomers having the same molecular formula. This was observed both for oligosaccharide precursor and product ions. In addition, mobilities of both [M – H]− and [M + Cl]− ions, formed by adding NH4OH or NH4Cl to the electrospray solvent, were examined and compared for selected oligosaccharide-alditols. Better separation among structural isomers appeared to be achieved for some [M + Cl]− anions.

The current analytical method for the determination of fatty acids is by GC-FAMEs (gas chromatography-Fatty Acid Methyl Esters). GC-FAMEs consist of a time-consuming esterification process to increase the volatility and decrease the polarity of fatty acids before gas chromatographic separation. The work reported here evaluates ion mobility spectrometry as alternative method for the analysis of FAMEs. Electrospray ionization—ion mobility spectrometry (ESI-IMS) enabled the rapid qualitative analysis of both the non-volatile and volatile fatty acids (FAs) and FAMEs. For the volatile FAME compounds, a 63Ni ionization source was also evaluated. While individual analytes worked well, a mixture of the FAME analytes experienced ion suppression. Introduction of a FAME analyte mixture by electrospray-ionization improved both detection and separation. The introduction of the FAs by direct ESI with ion mobility separation, however, provided the best results producing a rapid method for the characterization of FAs that did not require derivatization. Reduced mobility values (K0) were reported for the first time for six FA analytes: heneicosanoic acid (1.03 ± 0.02 cm2V−1 s−1), cis-11-eicosenoic acid (1.07 ± 0.02 cm2V−1 s−1) oleic acid (1.13 ± 0.0 cm2V−1 s−1),cis-vaccenic acid (1.13 ± 0.02 cm2V−1 s−1), γ-linolenic acid (1.16 ± 0.02 cm2V−1 s−1), and lauric acid (1.31 ± 0.02 cm2V−1 s−1), as well as their corresponding FAME analytes: methyl heneicosanoate (0.90 ± 0.02 cm2V−1 s−1), methyl-cis-11-eicosenate (0.96 ± 0.02 cm2V−1 s−1), cis-11-vaccenic acid methyl ester (1.03 ± 0.02 cm2V−1 s−1), methyl oleate (1.05 ± 0.02 cm2V−1 s−1), methyl linolenate (1.12 ± 0.02 cm2V−1 s−1), methyl laurate (1.21 ± 0.02 cm2V−1 s−1).

Electrospray ionization ion mobility mass spectrometry (ESI-IMMS) was used to study the striatal metabolomes in a Parkinson’s like disease (PD-like) rat model. Striatal tissue samples from Berlin Druckrey IV (BD-IV) with PD-like disease 20 dpn-affected and 15 dpn-affected rats (dpn: days postnatal) were investigated and compared with age-matched controls. An ion mobility mass spectrometer (IMMS) produced multidimensional spectra with mass to charge ratio (m/z), ion mobility drift time, and intensity information for each individual metabolite. Principle component analysis (PCA) was applied in this study for pattern recognition and significant metabolites selection (68% data was modeled in PCA). Both IMMS spectra and PCA results showed that there were clear global metabolic differences between PD-like samples and healthy controls. Nine metabolites were selected by PCA and identified as potential biomarkers using the Human Metabolome Database (HMDB). One targeted metabolite in this study was dopamine. Selected-mass mobility analysis indicated the absence of dopamine in PD-like striatal metabolomes. A major discovery of this work, however, was the existence of an isomer of dopamine. By using ion mobility spectrometry, the dopamine isomer, which has not previously been reported, was separated from dopamine.

•The ratio of reduced ion mobilities is measured as a function of water content. It is suggested that it be used to determine gas-phase water content.•High precision ion mobility measurements.•Prediction of the clustering process of successive neutral waters around DMMP protonated monomer ion is supported by density functional theory calculations.•Prediction of the ion mobility cross-sections in N2 using the trajectory method.Ion mobility spectrometry is widely used in national defense areas, and field-deployed IMS units are subject to various environmental conditions; one of the most important and least controlled being the humidity of the sample and drift gas. Varying drift gas water content can significantly alter the drift time and reduce the mobility constant (K0 value) of the ion. While the effect of drift gas water content has been previously characterized, no means to quantitatively measure the water content of the drift gas under field conditions have been developed. In this work, using an IMS-TOFMS instrument capable of high precision (±0.005 cm2 V−1 s−1 or better) measurements of K0 values, we investigated the protonated monomer and proton-bound dimer ions of dimethyl methylphosphonate as standards that are sensitive and insensitive, respectively, to the formation of water cluster ions. It was found that the ratio of mobilities of these two ions could measure the water content of the drift gas in field-deployed instruments. When water vapor was added in the presence of an ammonia dopant, K0 was found to decrease as a function of water content to a lesser degree than under conditions without dopant. This study was conducted at atmospheric pressure and at temperatures from 30 °C to 150 °C. The experimental data were supported by complementary density functional theory calculations that examined the interactions of the DMMP monomer with successive number of waters. The reduced ion mobility cross-sections in N2 were subsequently predicted using the trajectory method.

A high resolution ion mobility spectrometer was interfaced to a Synapt G2 high definition mass spectrometer (HDMS) to produce IMMS–IMMS analysis. The hybrid instrument contained an electrospray ionization source, two ion gates, an ambient pressure linear ion mobility drift tube, a quadrupole mass filter, a traveling wave ion mobility spectrometer (TWIMS), and a time-of-flight mass spectrometer. The dual gate drift tube ion mobility spectrometer (DTIMS) could be used to acquire traditional IMS spectra but also could selectively transfer specific mobility selected precursor ions to the Synapt G2 HDMS for mass filtration (quadrupole). The mobility and mass selected ions could then be introduced into a collision cell for fragmentation followed by mobility separation of the fragment ions with the traveling wave ion mobility spectrometer. These mobility separated fragment ions are finally mass analyzed using a time-of-flight mass spectrometer. This results in an IMMS–IMMS analysis and provides a method to evaluate the isomeric heterogeneity of precursor ions by both DTIMS and TWIMS to acquire a mobility-selected and mass-filtered fragmentation pattern and to additionally obtain traveling wave ion mobility spectra of the corresponding product ions. This new IMMS2 instrument enables the structural diversity of carbohydrates to be studied in greater detail. The physical separation of isomeric oligosaccharide mixtures was achieved by both DTIMS and TWIMS, with DTIMS demonstrating higher resolving power (70–80) than TWIMS (30–40). Mobility selected MS/MS spectra were obtained, and TWIMS evaluation of product ions showed that isomeric forms of fragment ions existed for identical m/z values.

•Ion mobility-mass spectrometry (IMMS) has the capability to rapidly evaluate the isomeric heterogeneity of oligosaccharide mixtures on millisecond timescale.•Even after a single HPLC column, isomeric structures that were present in fractions could frequently be resolved as independent peaks using IMMS.•Ion mobility coupled to tandem stages of mass spectrometry enabled different sets of product ions to be assigned to different isomeric precursors within a given m/z pool.Rapid separation and independent analysis of isomeric species are needed for the structural characterization of carbohydrates in glycomics research. Ion mobility-mass spectrometry techniques were used to examine a series of isomeric neutral oligosaccharide-alditols derived from bovine submaxillary mucin. Several analytical techniques were employed: (1) off line separation of the oligosaccharide-alditol mixture by HPLC; (2) direct and rapid evaluation of isomeric heterogeneity of oligosaccharides by electrospray ionization-ion mobility-time of flight mass spectrometry; and (3) mobility-selected MS2 and MS3 to evaluate isomeric mobility peaks by dual gate ion mobility-tandem mass spectrometry. Multiple isomeric ion mobility peaks were observed for the majority of oligosaccharide-alditols, which was achieved on the millisecond time scale after LC separation. Fragmentation spectra obtained from the collision-induced dissociation of isomeric precursor ions could be essentially identical, or dramatically different for a given precursor m/z using the dual-gate ion mobility quadrupole ion trap mass spectrometer. This further confirmed the need for rapid physical resolution of isomeric precursor species prior to their tandem mass spectral analysis.

This study relates the first mass identification of mobility peaks associated with uranyl species. These uranyl species were introduced into the gas phase by electrospray ionization and detected by ion mobility-mass spectrometry (IM-MS) to obtain rapid chemical information from uranyl compounds. Uranyl compound analysis in nuclear forensic science is typically performed using alpha, gamma, and mass spectrometry after extensive sample preparation and purification. Although providing highly sensitive isotopic and concentration information, these methods do not provide chemical information during the initial stages of analysis. Ion mobility spectrometry, when coupled with mass spectrometry, provides chemical information, including mass-identified mobility values, for analyte identification. In this study, uranyl compounds were detected in both the positive and negative ionization modes by electrospray-ion mobility-time of flight mass spectrometry (ESI-IM-TOFMS). The results showed that the sample type influenced the analyte ions that formed in the negative mode and that ESI solvent composition was the main factor that influenced analyte ion formation in the positive mode analysis. These results indicate that ESI-IM-TOFMS can be used to obtain rapid, chemical information for the initial analysis of a sample containing uranyl compounds.Graphical abstractHighlights► Reduced mobility values can be obtained for uranyl compounds. ► The negative ionization mode can be used to distinguish uranyl acetate, uranyl nitrate, and uranyl chloride. ► ESI-IM-TOFMS can be used to obtain rapid, chemical information for the initial analysis of a sample containing uranyl compounds.

63Nickel radioactive ionization (63Ni) is the most common and widely used ion source for ion mobility spectrometry (IMS). Regulatory, financial, and operational concerns with this source have promoted recent development of non-radioactive sources, such as corona discharge ionization (CD), for stand-alone IMS systems. However, there has been no comparison of the negative ion species produced by all three sources in the literature. This study compares the negative reactant and analyte ions produced by three sources on an ion mobility-mass spectrometer: conventional 63Ni, CD, and secondary electrospray ionization (SESI). Results showed that 63Ni and SESI produced the same reactant ion species while CD produced only the nitrate monomer and dimer ions. The analyte ions produced by each ion source were the same except for the CD source which produced a different ion species for the explosive RDX than either the 63Ni or SESI source. Accurate and reproducible reduced mobility (K0) values, including several values reported here for the first time, were found for each explosive with each ion source. Overall, the SESI source most closely reproduced the reactant ion species and analyte ion species profiles for 63Ni. This source may serve as a non-radioactive, robust, and flexible alternative for 63Ni.Highlights► First comparison of the CD, SESI, and 63Ni ionization sources’ reactant ion chemistry. ► First comparison of the CD, SESI, and 63Ni ionization sources’ analyte ion chemistry. ► Previously unreported mass-identified, K0 values for ion species produced by explosives.

A high-throughput ion mobility mass spectrometer (IMMS) was used to rapidly separate and analyze peptides and glycopeptides derived from glycoproteins. Two glycoproteins, human α-1-acid glycoprotein and antithrombin III were digested with trypsin and subjected to electro-spray traveling wave IMMS analysis. No deglycosylation steps were performed; samples were complex mixtures of peptides and glycopeptides. Peptides and glycosylated peptides with different charge states (up to 4 charges) were observed and fell on distinguishable trend lines in 2-D IMMS spectra in both positive and negative modes. The trend line separation patterns matched between both modes. Peptide sequence was identified based on the corresponding extracted mass spectra and collision induced dissociation (CID) experiments were performed for selected compounds to prove class identification. The signal-to-noise ratio of the glycopeptides was increased dramatically with ion mobility trend line separation compared to non-trend line separation, primarily due to selection of precursor ion subsets within specific mobility windows. In addition, isomeric mobility peaks were detected for specific glycopeptides. IMMS demonstrated unique capabilities and advantages for investigating and separating glycoprotein digests in this study and suggests a novel strategy for rapid glycoproteomics studies in the future.

Matrix-assisted laser/desorption ionization (MALDI) time-of-flight mass spectrometry (TOF) has been investigated for use in the field of metabolomics; however, difficulties, mainly due to chemical interferences, are typically encountered. By coupling MALDI with ion mobility time-of-flight mass spectrometry (IMMS), isomers and isobars are resolved in mobility space reducing the chemical interference from matrix/background ions. MALDI-IMMS offers the advantages of high sensitivity, high throughput and low sample consumption. For this study, MALDI-IMMS was evaluated by monitoring metabolic changes in lymphatic fluid collected from fasting and fed rats. The number of metabolite features detected in the samples ranged between 1200 and 3400 depending on the duration between the feeding time and lymph sample collection. There were 747 metabolite features that were statistically analyzed by principal component analysis (PCA). From the 3-D score plots of PC1, PC2 and PC3 65 % of the original variation of the system was explained and the differences between the samples were demonstrated.

Security and military applications of analytical techniques demand a small, rugged, reliable instrument that has traditionally been served well by atmospheric pressure ion mobility spectrometry (IMS) systems. Modern threats stipulate these instruments must reliably operate in increasingly complex environments. Previous work has demonstrated that increasing the pressure of an IMS drift tube has the potential to increase the resolving power of IMS, but operation at low temperatures resulted in a leveling of the measured resolving power as a function of pressure. By creating a novel aperture grid/Faraday plate design, a high-pressure IMS (HPIMS) system has been created that maintains a resolving power efficiency of 80% regardless of the pressure applied to the cell. This allows previously unattainable resolving powers to be achieved utilizing a small (10.7 cm) IMS cell. Using high pressure, a stand-alone IMS cell of 10.7 cm length has demonstrated a resolving power of 102 when operated at 2.5 atm. An increase in peak-to-peak resolution was also noted as pressure increased. Finally, the slope of the resulting inverse mobility/pressure curve for a single analyte has been shown to be proportional to the collision-cross-section of the analyte of interest, providing a novel method for the calculation of collision-cross-section of target ions from the HPIMS data.

Liquid phase ion mobility spectrometry (LPIMS) has the potential to be miniaturized such that it can be incorporated into chip based technology, providing higher performance in terms of both detection sensitivity and resolving power than is currently available by other separation technologies such as gas phase IMS, chromatography, or electrophoresis. This work presents modeling, simulation, and experimental investigations to characterize the mobility of ions in a liquid phase. This study included the ionization, transfer, separation, and detection of ions in non-electrolyte liquids. Using a resistive glass tube, mobility spectra were obtained by pulsed ionization for several different analytes, namely, tetramethylammonium chloride, tetrabutylammonium chloride, and dimethyl methylphosphonate (DMMP). Ion separation was demonstrated by separating solvent ions from the ions generated from the test compounds. Simulation and theoretical resolving power calculations were made to validate the experimental mobility measurements. A parametric study on the dependence of IMS resolving power on drift length, voltage across drift cell, and pulse width determined the requirements for designing a miniaturized IMS system, approximately the centimeter scale, with high performance, resolving power approaching 100 or higher. Mobility spectra are used for the first time to determine the diffusion coefficients of ions in a liquid.

Monosaccharide structural isomers including sixteen methyl-d-glycopyranosides and four methyl-N-acetylhexosamines were subjected to ion mobility measurements by electrospray ion mobility mass spectrometry. Two ion mobility-MS systems were employed: atmospheric pressure drift tube ion mobility time-of-flight mass spectrometry and a Synapt G2 HDMS system which incorporates a low pressure traveling wave ion mobility separator. All the compounds were investigated as [M + Na]+ ions in the positive mode. A majority of the monosaccharide structural isomers exhibited different mobility drift times in either system, depending on differences in their anomeric and stereochemical configurations. In general, drift time patterns (relative drift times of isomers) matched between the two instruments. Higher resolving power was observed using the atmospheric pressure drift tube. Collision cross section values of monosaccharide structural isomers were directly calculated from the atmospheric pressure ion mobility experiments, and a collision cross section calibration curve was made for the traveling wave ion mobility instrument. Overall, it was demonstrated that ion mobility-mass spectrometry using either drift tube or traveling wave ion mobility is a valuable technique for resolving subtle variations in stereochemistry among the sodium adducts of monosaccharide methyl glycosides.

All atmospheric pressure ion detectors, including photo ionization detectors, flame ionization detectors, electron capture detectors, and ion mobility spectrometers, utilize Faraday plate designs in which ionic charge is collected and amplified. The sensitivity of these Faraday plate ion detectors are limited by thermal (Johnson) noise in the associated electronics. Thus approximately 106 ions per second are required for a minimal detection. This is not the case for ion detection under vacuum conditions where secondary electron multipliers (SEMs) can be used. SEMs produce a cascade of approximately 106 electrons per ion impinging on the conversion dynode. Similarly, photomultiplier tubes (PMTs) can generate approximately 106 electrons per photon. Unlike SEMs, however, PMTs are evacuated and sealed so that they are commonly used under atmospheric pressure conditions. This paper describes an atmospheric pressure ion detector based on coupling a PMT with light emitted from ion–ion neutralization reactions. The normal Faraday plate collector electrode was replaced with an electrode “needle” used to concentrate the anions as they were drawn to the tip of the needle by a strong focusing electric field. Light was emitted near the surface of the electrode when analyte ions were neutralized with cations produced from the anode. Although radiative-ion–ion recombination has been previously reported, this is the first time ions from separate ionization sources have been combined to produce light. The light from this radiative-ion–ion-neutralization (RIIN) was detected using a photon multiplier such that an ion mobility spectrum was obtained by monitoring the light emitted from mobility separated ions. An IMS spectrum of nitroglycerin (NG) was obtained utilizing RIIN for tranducing the mobility separated ions into an analytical signal. The implications of this novel ion transduction method are the potential for counting ions at atmospheric pressure and for obtaining ion specific emission spectra for mobility separated ions.

The comparison of nanospray and microspray ionizations for detecting mixtures of compounds by ion mobility spectrometry has been investigated for sensitivity, ion transmission through a drift tube, and ion suppression effects when used as an ionization source for ambient pressure ion mobility spectrometry (IMS). Several articles have demonstrated that nano-electrospray ionization mass spectrometry (n-ESI-MS) has improved sensitivity, provides less background noise, and lower limits of detection than micro-electrospray ionization (μ-ESI) for IMS. Most importantly, data from n-ESI-MS is concentration-sensitive. Our laboratory previously published an article that observed a striking result when μ-ESI-IMS was investigated for a single compound in the positive ion mode. The data reported was mass-sensitive. In this new investigation, we have investigated mixtures, and experiments were designed to evaluate the effect of sensitivity, ion transmission and ion suppressions in μ-ESI-IMS and n-ESI-IMS. At an electrospray flow rate in the μL min−1 range, compounds with higher proton affinities responded best while at the nanospray flow rates of nL min−1, relative responses were more equal. This study observed that a decreased ESI flow rate resulted in a decreased ion signal. These trends demonstrated less sensitivity for ESI-IMS at reduced flow rates but suggest better quantification. At higher flow rates, relative ionization efficiencies were still uniform for all the components studied individually and in mixtures and sensitivity improved by about 78%. Concentration studies showed that at high concentrations, ion detection efficiencies were uniform at about 33% for all compounds studied individually and in mixtures. At low concentrations, the detection efficiency varied from 31% to 86%, depending on the proton affinity of the component in the mixture. Ion transmission through the IMS tube measured with a segmented Faraday detector that was incorporated into the IMS design indicated that most of the ion current for mixtures was transported through the IMS tube with a radius of less than 18 mm for both positive and negative ion modes.

Chemical standards are used to calibrate ion mobility spectrometers (IMS) for accurate and precise identification of target compounds. Research over the past 30 years has identified several positive and negative mode compounds that have been used as IMS standards. However, the IMS research community has not come to a consensus on any chemical compound(s) for use as a reference standard. Also, the reported K0 values for the same compound analyzed on several IMS systems can be inconsistent. In many cases, mobility has not been correlated with a mass identification of an ion.The primary goal of this work was to provide mass-identified mobility (K0) values for standards. The results of this work were mass-identified K0 values for positive and negative mode IMS chemical standards. The negative mode results of this study showed that TNT is a viable negative mode reference standard. New temperature-dependent K0 values were found by characterizing drift gas temperature and water content; several examples were found of temperature-dependent changes for the ion species of several standards. The overall recommendation of this study is that proposed IMS standards should have temperature-dependent K0 values quoted in the literature instead of using a single K0 value for a compound.Highlights► The first simultaneously mass-identified mobility values for the proposed IMS standards. ► Previously unreported temperature-dependent changes to the ion species for several standards. ► Previously unreported temperature-dependent reduced mobility value changes for several negative mode IMS standards

Ion mobility spectrometry (IMS) is a rapid, gas-phase separation technique that exhibits excellent separation of ions as a standalone instrument. However, IMS cannot achieve optimal separation power with both small and large ions simultaneously. Similar to the general elution problem in chromatography, fast ions are well resolved using a low electric field (50−150 V/cm), whereas slow drifting molecules are best separated using a higher electric field (250−500 V/cm). While using a low electric field, IMS systems tend to suffer from low ion transmission and low signal-to-noise ratios. Through the use a novel voltage algorithm, some of these effects can be alleviated. The electric field was swept from low to high while monitoring a specific drift time, and the resulting data were processed to create a ‘voltage-sweep’ spectrum. If an optimal drift time is calculated for each voltage and scanned simultaneously, a spectrum may be obtained with optimal separation throughout the mobility range. This increased the resolving power up to the theoretical maximum for every peak in the spectrum and extended the peak capacity of the IMS system, while maintaining accurate drift time measurements. These advantages may be extended to any IMS, requiring only a change in software.

Ion mobility spectrometry (IMS) has become the most widely used technology for trace explosives detection. A key task in designing IMS systems is to balance the explosives detection performance with size, weight, cost, and safety of the instrument. Commercial instruments are, by and large, equipped with radioactive 63Ni ionization sources which pose inherent problems for transportation, safety, and waste disposal regulation. An alternative to a radioactive source is a corona discharge ionization source, which offers the benefits of simplicity, stability, and sensitivity without the regulatory problems. An IMS system was designed and built based on modeling and simulation with the goal to achieve a lightweight modular design that offered high performance for the detection of trace explosives using a corona ionization source. Modeling and simulations were used to investigate design alternatives and optimize parameters. Simulated spectra were obtained for 2,4,6-trinitrotoluene (TNT) and cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) and showed good agreement with experimentally measured spectra using a corona ionization source. The reduced mobilities for TNT and RDX obtained with corona ionization were 1.53 and 1.46 cm2/(V s), respectively, and this agreed well with literature values.

A novel analytical method, called Liquid Phase Ion Mobility Spectrometry (LiPIMS) was demonstrated, where aqueous phase analytes were ionized and introduced into non-aqueous liquids, transported by an external electric field from the point of generation to a collection electrode. Ions were produced from a unique liquid phase ionization process, called Electrodispersion Ionization. Spectra of analyte ions illustrated the potential of LiPIMS as a new separation technique. Experimental data showed that electrodispersion ionization was effective in generating nanoampere level of ion current in hexane and benzene from aqueous samples. By controlling the ionization voltage in relation to the sample flow rate, it was possible to operate the electrodispersion ionization source in both continuous and pulsed ionization modes. Unique LiPIMS spectra of aqueous samples of tetramethylammonium bromide, tetrabutylammonium bromide and bradykinin were presented and their respected liquid phase ion mobility values were determined.

Detecting early stages of cancer has been a challenge for analytical methods. Even with the advances in mammography and prostate specific antigen (PSA) testing the number of false positives and negatives is still significant. Cancer cell lines provide realistic simulations to assess detection technologies for different stages and types of cancer. Metabolomics, the measure of end products of all biological processes, is a recent addition to the field of systems biology and can be targeted towards early disease detection. For this study, the metabolomes of three cancer cell lines, two prostate (DU145 and PC3) and one melanoma (A375), were investigated by an ion mobility mass spectrometer (IMMS) for both positive and negative ion detection mode. IMMS produced multidimensional data that includes m/z, mobility and intensity for each ion detected in the sample. In order to see differences between the cancer cell lines, principal components analysis (PCA), a multi-variant technique used to pull patterns out of the data, was used in conjunction with the IMMS data. The sample patterns from the PCA were observed in the score plot and the individual metabolites that contributed the most to the model were shown in the loadings plot. For positive mode 127 metabolite ions were statistically analyzed and in the negative mode 115 metabolite ions were analyzed. PCA score plots were able to model 98% and 87% of the original data for positive and negative mode, respectively. The metabolite ions from the loadings plot were tentatively identified based on m/z.

Increasing the dimensionality of an analysis enables more detailed and comprehensive investigations of complex mixtures. One dimensional separation techniques like gas chromatography (GC) and ion mobility spectrometry (IMS) provide limited chemical information about complex mixtures. The combination of GC, ion mobility spectrometry, and time-of-flight mass spectrometry (GC-IM-TOFMS) provides three-dimensional separation of complex mixtures. In this work, a hybrid GC-IM-TOFMS with a secondary electrospray ionization (SESI) source provided four types of analytical information: GC retention time, ion mobility drift time, mass-to-charge ratios, and ion intensity. The use of secondary electrospray ionization enables efficient and soft ionization of gaseous sample vapors at atmospheric pressure. Several complex mixtures, including lavender and peppermint essential oils, were analyzed by GC-SESI-IM-TOFMS. The resulting 3D data from these mixtures, each containing greater than 50 components, were plotted as 3D projections. In particular, post-processed data plotted in three dimensions showed that many mass selected GC peaks were resolved into different ion mobility peaks. This technique shows clear promise for further in-depth analyses of complex chemical and biological mixtures.

Ion mobility−time-of-flight mass spectrometry (IM−TOFMS) was used to identify and correlate response ions associated with three black powder samples by mass and mobility. Vapors produced by thermal desorption of the black powders were ionized by a 63Ni source; subsequent response ions were separated and identified using IM−TOFMS. The same response ions were found for each black powder regardless of geographic origin. The most intense mass and mobility peaks were attributed to ionic forms of sulfur allotropes (32Sn−, where n = 1−5). Vapor samples from GOEX black powder were also analyzed by two stand-alone ion mobility spectrometry systems, yielding an average reduced mobility value (Ko) of 2.28 ± 0.02 cm2 V−1 s−1 for black powder across all three instruments.

The design of a new ion mobility mass spectrometer (IM-MS) is presented. This new design features an ambient-pressure resistive glass ion mobility drift tube (RGIMS) coupled to a high-resolution time-of-flight mass spectrometer (TOFMS) by an enhanced interface that includes two segmented quadrupoles. The interface design demonstrates an increase in sensitivity while maintaining high resolving power typically achieved for ambient-pressure IMS drift tubes. Performance of the prototype instrument was evaluated and the analytical figures of merit for standard solutions as well as complex samples such as human blood were determined. For a 3 μM solution of caffeine, the peak was collected in 36 s and gave a response of 10 counts/s. The detection limit (defined as 1 count/s) was calculated to be 300 nM concentration of caffeine from the response rate from the 36 s run. Controlled fragmentation of caffeine was achieved through adjustment of voltages applied on the interface lenses. Over 300 tentative metabolites were detected in human blood along with 80 isomers/isobars with ion counts >5. Isotope ratios from extracted mass spectra of selected mobility peaks were used to identify selected metabolite compounds. High separation power for both IMS (resolving power, td/Δtw1/2, was 85) and MS (mass resolving power, m/Δm, maximum was 7000 with a mass accuracy between 2 and 10 ppm) was measured. Developed software for data acquisition, control and display allowed flexibility in instrument control, data evaluation and visualization.

Detection limits and reduced mobilities for 12 ribonucleotides and 4 ribonucleosides were measured by ambient pressure electrospray ionization–ion mobility spectrometry (ESI–IMS). With the instrument used in this study it was possible to separate some of these compounds within mixtures. Detection limits reported for ribonucleotides and ribonucleosides ranged from 15 to 300 pmol and the reduced mobilities ranged from 41 to 56 suggesting that ambient pressure ESI–IMS may be used for their rapid and sensitive separation and detection. This report demonstrates that it was possible to use ion mobility spectrometry (IMS) to obtain a spectrum for the separation of nucleotides and nucleosides in less than 1 min. The application holds great promise for nucleotide analysis in the area of separating DNA fragments in genome sequencing and also for forensics DNA typing examinations used for the identification of blood stains in crime scenes and paternity testing.

In ion mobility spectrometry (IMS), reduced mobility values (K0) are used as a qualitative measure of gas phase ions, and are reported in the literature as absolute values. Unfortunately, these values do not always match with those collected in the field. One reason for this discrepancy is that the buffer gas may be contaminated with moisture or other volatile compounds. In this study, the effect of moisture and organic contaminants in the buffer gas on the mobility of IMS standards and analytes was investigated for the first time using IMS directly coupled to mass spectrometry. 2,4-Dimethylpyridine, 2,6-di-tert-butylpyridine (DTBP), and tetrabutylammonium, tetrapropylammonium, tetraethylammonium, and tetramethylammonium chlorides were used as chemical standards. In general, the mobility of IMS standard product ions was not affected by small amounts of contamination while the mobilities of many analytes were affected. In the presence of contaminants in the buffer gas, the mobility of analyte ions is often decreased by forming ion–molecule clusters with the contaminant. To ensure the measurement of accurate reduced mobility values, two IMS standards are required: an instrument and a mobility standard. An instrument standard is not affected by contaminants in the buffer gas, and provides an accurate measurement of the instrumental parameters, such as voltage, drift length, pressure, and temperature. The mobility standard behaves like an analyte ion in that the compound's mobility is affected by low levels of contamination in the buffer gas. Prudent use of both of these standards can lead to improved measurement of accurate reduced mobility values.

The mobilities of a set of common α-amino acids, four tetraalkylammonium ions, 2,4-dimethyl pyridine (2,4-lutidine), 2,6-di-tert-butyl pyridine (DTBP), and valinol were determined using electrospray ionization-ion mobility spectrometry-quadrupole mass spectrometry (ESI-IMS–QMS) while introducing 2-butanol into the buffer gas. The mobilities of the test compounds decreased by varying extents with 2-butanol concentration in the mobility spectrometer. When the concentration of 2-butanol increased from 0.0 to 6.8 mmol m−3 (2.5 × 102 ppmv), percentage reductions in mobilities were: 13.6% (serine), 12.2% (threonine), 10.4% (methionine), 10.3% (tyrosine), 9.8% (valinol), 9.2% (phenylalanine), 7.8% (tryptophan), 5.6% (2,4-lutidine), 2.2% (DTBP), 1.0% (tetramethylammonium ion, TMA, and tetraethylammonium ion, TEA), 0.0% (tetrapropylammonium ion, TPA), and 0.3% (tetrabutylammonium ion, TBA). These variations in mobility depended on the size and steric hindrance on the charge of the ions, and were due to the formation of large ion-2-butanol clusters. This selective variation in mobilities was applied to the resolution of a mixture of compounds with similar reduced mobilities such as serine and valinol, which overlapped in N2-only buffer gas in the IMS spectrum. The relative insensitivity of tetraalkylammonium ions and DTBP to the introduction of 2-butanol into the buffer gas was explained by steric hindrance of the four alkyl substituents in tetraalkylammonium ions and the two tert-butyl groups in DTBP, which shielded the positive charge of the ion from the attachment of 2-butanol molecules. Low buffer gas temperatures (100 °C) produced the largest reductions in mobilities by increasing ion-2-butanol interactions and formation of clusters; high temperatures (250 °C) prevented the formation of clusters, and no reduction in ion mobility was obtained with the introduction of 2-butanol into the buffer gas. Low temperatures and high concentrations of 2-butanol produced a series of ion clusters with one to three 2-butanol molecules in compounds without steric hindrance. Clusters of two and three molecules of 2-butanol were also visible. Ligand-saturation on the positive ions with 2-butanol molecules occurred at high concentrations of modifier (6.8 mmol m−3 at 150 °C); when saturated, no further reduction in mobility occurred when 2-butanol was introduced into the buffer gas.Graphical abstractIon mobilities were determined using IMS–MS by injecting 2-butanol into the buffer gas. Ion mobilities decreased to different extents due to clustering with 2-butanol, resolving compounds with similar mobilities.Research highlights▶ Mobilities of ions were determined using IMS–MS while introducing 2-butanol into the buffer gas. ▶ The mobilities of the test ions decreased by varying extents. ▶ These variations in mobility depended on the size and steric hindrance on the charge of the ions. ▶ These variations in mobility were due to the formation of large ion-2-butanol clusters. ▶ This selective variation in mobilities was applied to the resolution of a mixture of compounds.

A high-resolution ion mobility time-of-flight mass spectrometer with electrospray ionization source (ESI-IM-MS) was evaluated as an analytical method for rapid analysis of complex biological samples such as human blood metabolome.The hybrid instrument (IM-MS) provided an average ion mobility resolving power of ∼90 and a mass resolution of ∼1500 (at m/z 100). A few μL of whole blood was extracted with methanol, centrifuged and infused into the IM-MS via an electrospray ionization source. Upon IM-MS profiling of the human blood metabolome approximately 1100 metabolite ions were detected and 300 isomeric metabolites separated in short analyses time (30 min). Estimated concentration of the metabolites ranged from the low micromolar to the low nanomolar level. Various classes of metabolites (amino acids, organic acids, fatty acids, carbohydrates, purines and pyrimidines, etc.) were found to form characteristic mobility-mass correlation curves (MMCCs) that aided in metabolite identification. Peaks corresponding to various sterol derivatives, estrogen derivatives, phosphocholines, prostaglandins, and cholesterol derivatives detected in the blood extract were found to occupy characteristic two-dimensional IM-MS space. Low abundance metabolite peaks that can be lost in MS random noise were resolved from noise peaks by differentiation in mobility space. In addition, the peak capacity of MS increased sixfold by coupling IMS prior to MS analysis.

The effects of above-ambient pressure on ion mobility on resolving power, resolution, and ion current were investigated using a small, stand-alone ion mobility spectrometer (IMS). This work demonstrates the first example of ion mobility spectrometry at pressures above ambient. Ion mobility spectra of chemical warfare agent (CWA) stimulant dimethyl methylphosphonate (DMMP) and several other standard compounds are shown for superambient conditions. The IMS was operated at pressures from 700 to 4560 Torr. An optimal resolving power was obtained at a specific voltage as a function of pressure, with higher optimal resolving powers obtained at higher voltages, as predicted from standard IMS theory. At high pressures, however, resolving power did not increase as much as theory predicted, presumably due to ion clustering. Nevertheless, an increase in pressure was found to improve resolution in IMS. One example where high pressure improved resolution was the separation of cyclohexylamine (K0 = 1.83) and 2-hexanone (K0 = 1.86) (where K0 is the reduced mobility value). The product ions of these two compounds could not be separated at ambient pressure but could be nearly baseline separated when the pressure of the buffer gas was raised to 2280 Torr. Total ion current was also examined at pressures from ambient up to 4560 Torr. Total ion current, when investigated with pressure, was found to reach a maximum, initially rising with increased pressure.

Ambient pressure ion mobility time-of-flight mass spectrometry (IMMS) has recently emerged as a rapid and efficient analytical technique for applications to metabolomics. An important application of metabolomics is to monitor metabolome shifts caused by stress due to toxin exposure, nutritional changes, or disease. The research presented in this paper uses IMMS to monitor metabolic changes in rat lymph fluid caused by dietary stresses over time. Extracts of metabolites found in the lymph fluid collected from dietary stressed rats were subjected to analysis by electrospray (ESI) IMMS operated both in positive and negative ion detection mode. Metabolites detected were tentatively identified based on their mass to charge ratio (m/z). In one sample, 1180 reproducible tentative metabolite ions were detected in negative mode and 1900 reproducible tentative metabolite ions detected in positive mode. Only biologically reproducible ions, defined as metabolite ions that were measured in different rats under the same treatment, were analyzed to reduce the complexity of the data. A metabolite peak list including m/z, mobility, and intensity generated for each metabolome was used to perform principle component analysis (PCA). Dynamic changes in metabolomes were investigated using principle components PC1 and PC2 that described 62% of the variation of the system in positive mode and 81% of the variation of the system in negative mode. Analysis of variance (ANOVA) was performed for PC1 and PC2 and means were statistically evaluated. Profiles of intensities were compared for tentative metabolite ions detected at different times before and after the rats were fed to identify the metabolites that were changing the most. Mobility-mass correlation curves (MMCC) were investigated for the different classes of compounds.

In the pharmaceutical industry, there are increasing requirements for analytical methods in quality assessment for the production of drugs. In this investigation, ion mobility spectrometry (IMS) was used for the rapid qualitative separation and identification of active ingredients in generic over-the-counter drugs and food additives in beverages. The active ingredients determined in drugs were acetaminophen, aspartame, bisacodyl, caffeine, dextromethorphan, diphenhydramine, famotidine, glucosamine, guaifenesin, loratadine, niacin, phenylephrine, pyridoxine, thiamin, and tetrahydrozoline. Aspartame and caffeine were determined in beverages. Fourteen over-the-counter drugs and beverages were analyzed. Analysis times below 10 s were obtained for IMS, and reduced mobilities were reported for the first time for 12 compounds. A quadrupole mass spectrometer coupled to a mobility spectrometer was used to assure a correct peak assignation. The combination of fast analysis, low cost, and inexpensive maintenance of IMS instruments makes IMS an attractive technique for the qualitative determination of the active ingredients in over-the-counter drugs and food additives in manufacture quality control and cleaning verification for the drug and food industries.

The rapid separation of isomeric precursor ions of oligosaccharides prior to their analysis by mass spectrometry to the nth power (MSn) was demonstrated using an ambient pressure ion mobility spectrometer (IMS) interfaced with a quadrupole ion trap. Separations were not limited to specific types of isomers; representative isomers differing solely in the stereochemistry of sugars, in their anomeric configurations, and in their overall branching patterns and linkage positions could be resolved in the millisecond time frame. Physical separation of precursor ions permitted independent mass spectra of individual oligosaccharide isomers to be acquired to at least MS3, the number of stages of dissociation limited only practically by the abundance of specific product ions. IMS–MSn analysis was particularly valuable in the evaluation of isomeric oligosaccharides that yielded identical sets of product ions in tandem mass spectrometry experiments, revealing pairs of isomers that would otherwise not be known to be present in a mixture if evaluated solely by MS dissociation methods alone. A practical example of IMS–MSn analysis of a set of isomers included within a single high-performance liquid chromatography fraction of oligosaccharides released from bovine submaxillary mucin is described.

Although diffusion theory predicts that IMS resolving power increases with the square root of the voltage applied across the drift tube, in practice, there exists an optimum voltage above which resolving power decreases. This optimum voltage was determined to be both compound and initial ion pulse width dependent. A “conditional” resolving power equation is introduced that can be used to quickly approximate realistic resolving powers for specific instrumental operating parameters and compounds. Using four common environmental contaminants (trichloroethylene, tetrachloroethylene, methyl tert-butyl ether, methyl isobutyl ketone), diffusion-limited (theoretical), Rd, conditional, Rc, and actual (or measured), Rm, IMS resolving powers were determined and compared for a small IMS instrument designed for subsurface measurements. Detection limits determined at the optimal resolving power for the environmental contaminants ranged from 18 parts per trillion volume-to-volume (pptv) to 80 parts per billion volume-to-volume (ppbv). The maximal measured resolving power for our small, ambient-pressure stand-alone IMS ranged from 42 to 54, yielding an IMS resolving power efficiency, defined as Rm/Rc × 100%, of 56−74% of the maximal conditional resolving power possible.

Analysis of hair is often applied to assess drug abuse history, exposure to environmental and industrial pollutants, heavy metals, gestational drug exposure and various other screening purposes. This manuscript reports the application of ambient pressure ion mobility spectrometry mass spectrometry (IMMS) with electrospray ionization (ESI) source as a rapid analytical tool for hair analysis. The study demonstrated that ion mobility spectrometry (IMS) as a pre-separation technique prior to analysis by mass spectrometry (MS) provides detection and determination of compounds of interest present in hair at nano-molar concentration level. After extraction of analytes from hair, the ESI-IMMS method of analysis does not require the derivatization or sample treatment that is often required for other separation methods such as gas chromatography. One advantage of IMS over chromatography separation is that resolving powers are similar to those in GC and much greater than those possible by liquid chromatography. In addition, separation speed is faster than both gas and liquid chromatographic methods. Four of the nine hair samples anonymously donated by customers at a local hair salon tested positive for caffeine and two of the four samples that tested positive for caffeine also tested positive for nicotine. A positive response based on mass analysis for methamphetamine was obtained for one of the hair samples. Further investigation using the mobility data demonstrated that the response was a false positive and that it may have occurred from the use of a hair gel. This article reports the potential of IMMS as an analytical technique for rapid and routine screening of hair samples, cosmetics, and pharmaceuticals.

Ion Mobility Mass Spectrometry (IMMS) was evaluated as an analytical method for metabolic profiling. The specific instrument used in these studies was a direct infusion (DI)-electrospray ionization (ESI)—ambient pressure ion mobility spectrometer (APIMS) coupled to a time-of-flight mass spectrometer (TOFMS). The addition of an ion mobility spectrometer to a mass spectrometer had several advantages over direct infusion electrospray mass spectrometry alone. This tandem instrument (ESI-IMMS) added a rapid separation step with high-resolution prior to mass spectrometric analysis of metabolite mixtures without extending sample preparation time or reducing the high through put potential of direct mass spectrometry. Further, IMMS also reduced the baseline noise common with ESI-MS analyses of complex samples and enabled rapid separation of isobaric metabolites. IMMS was used to analyze the metabolome of Escherichiacoli (E. coli), containing a collection of extremely diverse chemical compounds including hydrophobic lipids, inorganic ions, volatile alcohols and ketones, amino and non-amino organic acids, and hydrophilic carbohydrates. IMMS data were collected as two-dimensional spectra showing both mobility and mass of each ion detected. Using direct infusion ESI-IMMS of a non-derivatized methanol extract of an E. coli culture, more than 500 features were detected, of which over 200 intracellular metabolites were tentatively assigned as E. coli metabolites. This analytical method also allowed simultaneous separation of isomeric metabolic features.

This work demonstrated the potential of using a secondary drift gas of differing polarizability from the primary drift gas for confirmation of a positive response for drugs or explosives by ion mobility spectrometry (IMS). The gas phase mobilities of response ions for selected drugs and explosives were measured in four drift gases. The drift gases chosen for this study were air, nitrogen, carbon dioxide and nitrous oxide providing a range of polarizability and molecular weights. Four other drift gases (helium, neon, argon and sulfur hexafluoride) were also investigated but design limitations of the commercial instrument prevented their use for this application. When ion mobility was plotted against drift gas polarizability, the resulting slopes were often unique for individual ions, indicating that selectivity factors between any two analytes varied with the choice of drift gas. In some cases, drugs like THC and heroin, which are unresolved in air or nitrogen, were well resolved in carbon dioxide or nitrous oxide.

Carbohydrates are an extremely complex group of isomeric molecules that have been difficult to analyze in the gas phase by mass spectrometry because (1) precursor ions and product ions to successive stages of MSn are frequently mixtures of isomers, and (2) detailed information about the anomeric configuration and location of specific stereochemical variants of monosaccharides within larger molecules has not been possible to obtain in a general way. Herein, it is demonstrated that gas-phase analyses by direct combination of electrospray ionization, ambient pressure ion mobility spectrometry, and time-of-flight mass spectrometry (ESI-APIMS-TOFMS) provides sufficient resolution to separate different anomeric methyl glycosides and to separate different stereoisomeric methyl glycosides having the same anomeric configuration. Reducing sugars were typically resolved into more than one peak, which might represent separation of cyclic species having different anomeric configurations and/or ring forms. The extent of separation, both with methyl glycosides and reducing sugars, was significantly affected by the nature of the drift gas and by the nature of an adducting metal ion or ion complex. The study demonstrated that ESI-APIMS-TOFMS is a rapid and effective analytical technique for the separation of isomeric methyl glycosides and simple sugars, and can be used to differentiate glycosides having different anomeric configurations.

The use of negative ion monitoring mode with an atmospheric pressure ion mobility orthogonal reflector time-of-flight mass spectrometer [IM(tof)MS] to detect chemical warfare agent (CWA) degradation products from aqueous phase samples has been determined. Aqueous phase sampling used a traditional electrospray ionization (ESI) source for sample introduction and ionization. Certified reference materials (CRM) of CWA degradation products for the detection of Schedule 1, 2, or 3 toxic chemicals or their precursors as defined by the chemical warfare convention (CWC) treaty verification were used in this study. A mixture of six G-series nerve related CWA degradation products (EMPA, IMPA, EHEP, IHEP, CHMPA, and PMPA) and their related collision induced dissociation (CID) fragment ions (MPA and EPA) were found in each case to be clearly resolved and detected using the IM(tof)MS instrument in negative ion monitoring mode. Corresponding ions, masses, drift times, Ko values, and signal intensities for each of the CWA degradation products are reported.

Chemical warfare agent (CWA) simulants as well as their degradation and hydrolysis products were detected from surfaces using thermal desorption ion mobility spectrometry (TD-IMS). CWA simulant materials that closely mimic the chemical structures of real CWA G/V-type nerve and S-type vesicant simulants were used in this study. Reduced mobility constants (K0) in air were reported for 20 compounds studied. Spectra for sample materials as low as 1 ng deposited on a paper filter were produced for most of the compounds. Detection limits as low as 15 pg of sample material with a sensitivity of 3.2 × 102 ampere per gram (A g−1) were reported. TD-IMS, which is normally used for the detection of explosives and drugs of abuse, demonstrated the capability of separating and detecting mixtures of CWA simulants, degradation and hydrolysis products from surface samples. TD-IMS demonstrated clear advantages of speed, high throughput and versatility over chromatographic methods of analysis for detecting CWA simulants, degradation and hydrolysis products. Successful development of the technique may lead to a practical and simple sensor for CWA and related compounds that could be installed and used at sensitive locations around the USA and throughout the world.

An electrospray ionization atmospheric pressure ion mobility orthogonal reflector time-of-flight mass spectrometer (IM(tof)MS) that routinely achieves mobility and mass separation efficiencies in line with theoretical limits is reported. The maximum IM(tof)MS efficiency for a given instrumental design depends widely upon the various key parameters such as voltage, temperature, initial pulse width, interface and reflectron energies. Optimization of the current IM(tof)MS instrument, resulted in an IMS separation efficiency over 133,000 theoretical plates (a resolving power of 155) and a resolving power of 1200 for the TOFMS using a singly charged G/V-type chemical warfare agent (CWA) nerve simulant (dimethyl methylphosphonate (DMMP)) in less than 12 ms.

A series of isobaric disaccharide-alditols, four derived from O-linked glycoproteins, and select trisaccharides were rapidly resolved using tandem high resolution atmospheric pressure ion-mobility time-of-flight mass spectrometry. Electrospray ionization was used to create the gas-phase sodium adducts of each carbohydrate. Using this technique it was possible to separate up to three isobaric disaccharide alditols and three trisaccharides in the gas phase. Reduced mobility values and experimentally determined ion-neutral cross sections are reported for each sodium-carbohydrate complex. These studies demonstrated that ion mobility separations at atmospheric pressure can provide a high-resolution dimension for analysis of carbohydrate ions that is complementary to traditional mass spectral (m/z) ion analysis. Combining these independent principles for separation of ions provides a powerful new bioanalytical tool for the identification of isomeric carbohydrates.

This paper reports the first example of electrospray ionization (ESI) for the separation and detection of anions in aqueous solutions by ion mobility spectrometry (IMS). Standard solutions of arsenate, phosphate, sulfate, nitrate, nitrite, chloride, formate, and acetate were analyzed using ESI-IMS and distinct peak patterns and reduced mobility constants (K0) were observed for respective anions. Real world water samples were analyzed for nitrate and nitrite to determine the feasibility of using ESI-IMS as a rapid analytical method for monitoring nitrate and nitrite in water systems. The data showed satisfactory correlation between the measured value (∼0.16 ppm) and the reported maximum nitrate-nitrogen concentration (0.2 ppm) found in a local drinking water system. For on-site measurement applications, direct sample introduction and air as an alternate drift gas to nitrogen were evaluated. The identities of the nitrite and nitrate mobility peaks were verified by comparison of reduced mobility constants with mass identified nitrate and nitrite ions reported in literature. In the mixing ratio, a linear dynamic range of 3 orders of magnitude and instrument detection limits of 10 ppb for nitrate and 40 ppb for nitrite were obtained. The calibration curves showed r2 value of 0.98 and slope of 0.06 for nitrate and r2 value of 0.99 and slope of 0.11 for nitrite.

The utility of post-source decay (PSD) matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was investigated for the structural analysis of phosphatidylcholine (PC). PC did not produce detectable negative molecular ion from MALDI, but positive ions were observed as both [PC+H]+ and [PC+Na]+. The PSD spectra of the protonated PC species contained only one fragment corresponding to the head group (m/z 184), while the sodiated precursors produced many fragment ions, including those derived from the loss of fatty acids. The loss of fatty acid from the C-1 position (sn-1) of the glycerol backbone was favored over the loss of fatty acid from the C-2 position (sn-2). Ions emanating from the fragmentation of the head group (phosphocholine) included [PC+Na-59]+, [PC+Na-183]+ and [PC+Na-205]+, which corresponded to the loss of trimethylamine (TMA), non-sodiated choline phosphate and sodiated choline phosphate, respectively. Other fragments reflecting the structure of the head group were observed at m/z 183, 146 and 86. The difference in the fragmentation patterns for the PSD of [PC+Na]+ compared to [PC+H]+ is attributed to difference in the binding of Na+ and H+. While the proton binds to a negatively charged oxygen of the phosphate group, the sodium ion can be associated with several regions of the PC molecule. Hence, in the sodiated PC, intermolecular interaction of the negatively charged oxygen of the phosphate group, along with sodium association at multiple sites, can lead to a complex and characteristic ion fragmentation pattern. The preferential loss of sn-1 fatty acid group could be explained by the formation of an energetically favorable six-member ring intermediate, as apposed to the five-member ring intermediate formed prior to the loss of sn-2 fatty acid group.

Benzodiazepines are a commonly abused class of drugs; requiring analytical techniques that can separate and detect the drugs in a rapid time period. In this paper, the two-dimensional separation of five benzodiazepines was shown by electrospray ionization (ESI) ion mobility spectrometry (IMS)–mass spectrometry (MS). In this study, both the two dimensions of separation (m/z and mobility) and the high resolution of our IMS instrument enabled confident identification of each of the five benzodiazepines studied. This was a significant improvement over previous IMS studies that could not separate many of the analytes due to low instrumental resolution. The benzodiazepines that contain a hydroxyl group in their molecular structure (lorazepam and oxazepam) were found to form both the protonated molecular ion and dehydration product as predominant ions. Experiments to isolate the parametric reasons for the dehydration ion formation showed that it was not the result of corona discharge processes or the potential applied to the needle. However, the potential difference between the needle and first drift ring did influence both the relative intensity ratios of the two ions and the ion sensitivity.

Recent studies in electrospray ionization (ESI)/ion mobility spectrometry (IMS) have focussed on employing different drift gases to alter separation efficiency for some molecules. This study investigates four structurally similar classes of molecules (cocaine and metabolites, amphetamines, benzodiazepines, and small peptides) to determine the effect of structure on relative mobility changes in four drift gases (helium, nitrogen, argon, carbon dioxide). Collision cross sections were plotted against drift gas polarizability and a linear relationship was found for the nineteen compounds evaluated in the study. Based on the reduced mobility database, all nineteen compounds could be separated in one of the four drift gases, however, the drift gas that provided optimal separation was specific for the two compounds.

In recent years, the resolving power of ion mobility instruments has been increased significantly, enabling ion mobility spectrometry (IMS) to be utilized as an analytical separation technique for complex mixtures. In theory, decreasing the drift tube temperature results in increased resolution due to decreased ion diffusion. However, the heat requirements for complete ion desolvation with electrospray ionization (ESI) have limited the reduction of temperatures in atmospheric pressure ion mobility instruments. Micro-electrospray conditions were investigated in this study to enable more efficient droplet formation and ionization with the objective of reducing drift tube temperatures and increasing IMS resolution. For small molecules (peptides), the drift tube temperature was reduced to ambient temperature with good resolution by employing reduced capillary diameters and flow rates. By employing micro-spray conditions, experimental resolution values approaching theoretically predicted resolution were achieved over a wide temperature range (30 to 250 °C). The historical heat requirements of atmospheric pressure IMS due to ESI desolvation were eliminated due to the use of micro-spray conditions and the high-resolution IMS spectra of GLY-HIS-LYS was obtained at ambient temperature. The desolvation of proteins (cytochrome c) was found to achieve optimal resolution at temperatures greater than 125 °C. This is significantly improved from earlier IMS studies that required drift tube temperatures of 250°C for protein desolvation.

A novel analysis of explosives via the coupling of an airline passenger personnel portal with a high-flow (HF), high-resolution (HR) ion mobility spectrometry (IMS) was shown for the first time. The HF–HR–IMS utilized a novel ion aperture grid design with a 63Ni ionization source while operating at ambient pressure in the positive ion mode at 200 °C. The HF–HR–IMS response characteristics of 2,4,6-trinitrotoluene (TNT), 4,6-dinitro-o-cresol (4,6DNOC), and cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) were investigated. Modifications made to the HF–HR–IMS exhaust and ionization source created an 800% increase in the total ion current (TIC), from 0.85 to 6.8 nA. This translated into a 65% ion response increase for TNT when compared with a traditional IMS. A mixture of TNT and (4,6DNOC) was used to successfully demonstrate the resolving power of the species with similar reduced mobility constants (Ko), 1.54 and 1.59, respectively. The reactant ion (H2O)nH+, peak was also used to measure the resolving power of the spectrometer while varying the internal diameter of three different aperture openings from 1.00 to 3.54cm. This provided a resolving power range of 50–60, double that typically achievable by commercial IMS instruments. Most important, these changes made in this new instrumental design can be implemented to all existing and future IMS's to greatly enhance the achievable IMS resolving power.

The use of ion mobility spectrometry systems to detect explosives in high security situations creates a need to determine compounds that interfere and may compromise accurate detection. This is the first study to identify possible interfering air contaminants common in airport settings by IMS. Seventeen suspected contaminants from four major sources were investigated. Due to the ionization selectivity gained by employing chloride reactant ion chemistry, only 7 of the 17 compounds showed an IMS response. Of those seven compounds, only 4,6-dinitro-o-cresol (4,6DNOC) was found to have a similar mobility to 2,4,6-trinitrotoluene (TNT) with Ko values of 1.55 and 1.50 cm2 V−1 s−1, respectively. Although baseline resolution between TNT and 4,6DNOC was not achieved, the drift time for TNT was still easily identified. Alkyl-nitrated phenols, due to acidic fog, responded the strongest in the IMS. The effect of contamination on TNT sensitivity was investigated. Charge competition between TNT and 2,4-dinitrophenol (2,4DNP) was found to occur and to effect TNT sensitivity.

The analysis of explosives with ion mobility spectrometry (IMS) directly from aqueous solutions was shown for the first time using an electrospray ionization technique. The IMS was operated in the negative mode at 250°C and coupled with a quadrupole mass spectrometer to identify the observed IMS peaks. The IMS response characteristics of trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), 2-amino-4,6-dinitrotoluene (2-ADNT), 4-nitrotoluene (4-NT), trinitrobenzene (TNB), cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), cyclo-tetramethylene-tetranitramine (HMX), dinitro-ethyleneglycol (EGDN) and nitroglycerine (NG) were investigated. Several breakdown products, predominantly NO2− and NO3−, were observed in the low-mass region. Nevertheless, all compounds with the exception of NG produced at least one ion related to the intact molecule and could therefore be selectively detected. For RDX and HMX the [M+Cl−]− cluster ion was the main peak and the signal intensities could be greatly enhanced by the addition of small amounts of sodium chloride to the sprayed solutions. The reduced mobility constants (K0) were in good agreement with literature data obtained from experiments where the explosives were introduced into the IMS from the vapor phase. The detection limits were in the range of 15–190 μg l−1 and all calibration curves showed good linearity. A mixture of TNT, RDX and HMX was used to demonstrate the high separation potential of the IMS system. Baseline separation of the three compounds was attained within a total analysis time of 6.4 s.

This paper describes the first application of reverse-polarity capillary zone electrophoresis for rapid and accurate determination of nitrate and nitrite in Hanford defense waste (HDW). The method development was carried out by using synthetic Hanford waste, followed by the analysis of four real HDW samples. Hexamethonium bromide (HMB) was used as an electroosmotic flow modifier in a borate electrolyte at pH 9.2 to decrease the electroosmotic flow, enhancing the speed and resolution of the analytical determination of nitrate and nitrite in high ionic strength HDW samples. The application of this capillary zone electrophoresis method, when compared with ion chromatography for two major components of HDW, nitrate and nitrite, slightly reduced analysis time, eliminated most pre-analysis handling of the highly radioactive sample, and cut analysis wastes by more than two-orders of magnitude. The migration times of nitrate and nitrite in the real HDW and the spiked HDW samples were within a precision of less than 3% relative standard deviation. The selectivity ratio test used for peak confirmation of the spiked samples was within 96% of the real sample. Method reliability was tested by spiking the matrix with 1.0 mM nitrate and nitrite. Recoveries for these spiked samples were 93–103%.

Since the introduction of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry the majority of research has focused on developing analytical methods for the qualitative determination of water soluble biomolecules such as proteins, peptides, carbohydrates, and oligonucleotides. This paper, however, reports the use of MALDI for the analysis of triacylglycerols and develops a new sample preparation method for nonpolar analytes. MALDI enables the rapid analyses of triacylglycerol (TAG) standards and mixtures of whole oils. The new method provides excellent shot to shot reproducibility, making quantification possible. Detection limits were in the mid femtomole range and the resolution was around 2000 which easily separated TAGs differing by one double bond. Sensitivity decreased with increasing molecular weight, causing biased results when analyzing complex mixtures with a significant range of molecular weight. In all cases only sodiated molecules and prompt losses of a fatty acid sodium salt were observed in the spectra. From this information it was possible to identify the three fatty acids on the glycerol backbone. Collision-induced dissociation was carried out on a triacylglycerol which proved to be useful for additional structural information, including the corroboration of the fatty acid components. With MALDI the percent compositions of TAGs in a standard olive oil was accurately determined. Finally, MALDI was used to examine the differences in lipid components between aged and fresh onion seeds, showing the potential of the technique for observing changes in lipid components in seeds.

Carbohydrates are an extremely complex group of isomeric molecules that have been difficult to analyze in the gas phase by mass spectrometry because (1) precursor ions and product ions to successive stages of MSn are frequently mixtures of isomers, and (2) detailed information about the anomeric configuration and location of specific stereochemical variants of monosaccharides within larger molecules has not been possible to obtain in a general way. Herein, it is demonstrated that gas-phase analyses by direct combination of electrospray ionization, ambient pressure ion mobility spectrometry, and time-of-flight mass spectrometry (ESI-APIMS-TOFMS) provides sufficient resolution to separate different anomeric methyl glycosides and to separate different stereoisomeric methyl glycosides having the same anomeric configuration. Reducing sugars were typically resolved into more than one peak, which might represent separation of cyclic species having different anomeric configurations and/or ring forms. The extent of separation, both with methyl glycosides and reducing sugars, was significantly affected by the nature of the drift gas and by the nature of an adducting metal ion or ion complex. The study demonstrated that ESI-APIMS-TOFMS is a rapid and effective analytical technique for the separation of isomeric methyl glycosides and simple sugars, and can be used to differentiate glycosides having different anomeric configurations.