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PubMed2006

Exploring crown ethers as shift reagents for ion mobility spectrometry.

A series of crown ethers, 12-crown-4, 15-crown-5, 18-crown-6, and dibenzo-30-crown-10, are examined as a possible means of shifting the mobilities of peptide ions. In this approach, a crown ether is added to a solution containing a mixture of peptides and is electrosprayed into the gas phase in order to create distributions of peptide-crown complexes. The ion complexes have different mobilities than the naked peptide ions, and the crown ether molecules appear to interact specifically with basic sites in the peptides thus providing some sequence selectivity. After the peptide-crown complexes are separated by ion mobility spectrometry, the ions can be collisionally activated to dissociate the complex (forming the naked peptide ions) prior to m/z analysis. The overall effect is that complex formation shifts peptide ions to different regions of the mobility spectrum, extending the ability to resolve components. The approach is illustrated by examining isobaric dipeptides as well as a combinatorial library containing 27 tripeptides. Cross sections for the series of crown ether ions and complexes that are observed are reported.

Crown Ethers↗
PubMed2004

High-field asymmetric waveform ion mobility spectrometry: a new tool for mass spectrometry.

High-field asymmetric waveform ion mobility spectrometry (FAIMS) is a new technology for ion separation at atmospheric pressure. This review introduces the reader to FAIMS, covering topics ranging from the fundamentals and extraction of physical parameters from the raw data, to applications of FAIMS extending from homeland security to environmental analysis to proteomics. The investigation of FAIMS as an ion pre-processing tool for mass spectrometry is in its infancy, but reports in the literature illustrate that FAIMS separates isobaric ions including diastereoisomers, separates isotopes, reduces background ions by isolating ions of interest, and simplifies spectra of complex mixtures by dividing the mixture into a series of simpler subsets of ions. Applications ranging from quantitative analysis of inorganic and organometallic compounds, to studies of the conformers of intact proteins, have been reported. This review is a launching point for further exploration of FAIMS.

Mass Spectrometry↗
PubMed2006

Gas-phase chiral separations by ion mobility spectrometry.

This article introduces the concept of chiral ion mobility spectrometry (CIMS) and presents examples demonstrating the gas-phase separation of enantiomers of a wide range of racemates including pharmaceuticals, amino acids, and carbohydrates. CIMS is similar to traditional ion mobility spectrometry, where gas-phase ions, when subjected to a potential gradient, are separated at atmospheric pressure due to differences in their shapes and sizes. In addition to size and shape, CIMS separates ions based on their stereospecific interaction with a chiral gas. In order to achieve chiral discrimination by CIMS, an asymmetric environment was provided by doping the drift gas with a volatile chiral reagent. In this study (S)-(+)-2-butanol was used as a chiral modifier to demonstrate enantiomeric separations of atenolol, serine, methionine, threonine, methyl alpha-glucopyranoside, glucose, penicillamine, valinol, phenylalanine, and tryptophan from their respective racemic mixtures.

Amino Acids↗
PubMed2005

The structure of gas-phase bradykinin fragment 1-5 (RPPGF) ions: an ion mobility spectrometry and H/D exchange ion-molecule reaction chemistry study.

Ion mobility-mass spectrometry (IM-MS) data is interpreted as evidence that gas-phase bradykinin fragment 1-5 (BK1-5, RPPGF) [M + H](+) ions exist as three distinct structural forms, and the relative abundances of the structural forms depend on the solvent used to prepare the matrix-assisted laser desorption ionization (MALDI) samples. Samples prepared from organic rich solvents (90% methanol/10% water) yield ions having an ion mobility arrival-time distribution (ATD) that is dominated by a single peak; conversely, samples prepared using mostly aqueous solvents (10% methanol/90% water) yield an ATD composed of three distinct peaks. The BK1-5 [M + H](+) ions were also studied by gas-phase hydrogen/deuterium (H/D) exchange ion-molecule reactions and this data supports our interpretation of the IM-MS data. Plausible structures for BK1-5 ions were generated by molecular dynamics (MD). Candidate MD-generated structures correlated to measured cross-sections suggest a compact conformer containing a beta-turn whereas a more extended, open form does not contain such an interaction. This study illustrates the importance of intra-molecular interactions in the stabilization of the gas-phase ions, and these results clearly illustrate that solution-phase parameters (i.e., MALDI sample preparation) greatly influence the structures of gas-phase ions.

Bradykinin↗
PubMed2006

Application of ion mobility spectrometry in cases of forensic interest.

Ion mobility spectrometry (IMS) has been known as an analytical technique since the late 1960s and early 1970s. To date, it has been successfully utilized for the detection of environmental pollutants, warfare agents, explosives, herbicides, pesticides, petroleum products as well as for the detection of prescription and illicit drugs. In this paper the authors describe the use of the IMS technology in cases of forensic interest in Salzburg, Austria. We report the use of the IMS methodology for the rapid analysis of hallucinogenic mushroom material as well as for the analysis of samples taken after an explosion. A new application of the IMS technology for the analysis of postmortem sweat samples for drugs is also presented.

Adult↗
PubMed2001

Direct determination of ultra-trace amounts of acetone by corona-discharge ion mobility spectrometry.

The capability of corona-discharge ion mobility spectrometry (CD-IMS) in the quantitative determination of acetone has been evaluated. Generally, in IMS the signal intensity of a product ion is not a linear function of the sample concentration. A linear calibration curve was, however, obtained by plotting ln(R0+/R0+-P+) against acetone concentration, where, R0+ is the original reactant ion density and P+ is the sum of all the product ion densities. The acetone detection limit was 60 ng m(-3) and its dynamic range was three orders of magnitude.

Journal Article↗
PubMed2004

Understanding and designing field asymmetric waveform ion mobility spectrometry separations in gas mixtures.

Field asymmetric waveform ion mobility spectrometry (FAIMS) has significant potential for post-ionization separations in conjunction with MS analyses. FAIMS fractionates ion mixtures by exploiting the fact that ion mobilities in gases depend on the electric field in a manner specific to each ion. Nearly all previous work has used pure gases, for which FAIMS fundamentals are understood reasonably well; however, unexpected phenomena observed in some gas mixtures (e.g., N(2)/CO(2)) but not in others (N(2)/O(2)) remain unexplained. Here, we introduce and experimentally test a universal model for FAIMS separations in mixtures, derived from formalisms that determine high-field mobilities in heteromolecular gases. Overall, the theoretical findings are consistent with data for N(2)/CO(2) (although quantitative discrepancies remain), while results for N(2)/O(2) fit Blanc's law, in agreement with measurements. Calculations for He/N(2) and He/CO(2) are also consistent with observations and suggest why adding He to the working gas generally enhances FAIMS performance. As predicted, mixtures of gases with extremely disparate molecular masses and collision cross sections, such as He/SF(6), exhibit spectacular non-Blanc effects, which greatly improve the resolution and peak capacity of technique. Understanding FAIMS operation in gas mixtures is expected to enable the rational design of media for both targeted and global analyses.

Carbon Dioxide↗
PubMed2006

Detection of gunpowder stabilizers with ion mobility spectrometry.

This study is the first reported ion mobility detection of ethyl centralite and diphenylamine (DPA) smokeless gunpowder stabilizers, together with the nitroso and nitro derivatives of diphenylamine. First, the applicability of the ion mobility spectrometry (IMS) for the substances of interest was determined. The existence of numerous peaks, both in positive and negative modes, clearly demonstrates the success of these experiments. All mono and di-nitro derivatives of DPA tested were detected with this method. Unfortunately, many of the ions generated were not accurately identified. However, reduced mobility constants representative of each ion generated under defined operating conditions could be used for purpose of compound identification. The method was then successfully tested on real gunpowder samples. By the use of IMS, we managed to establish a rapid, simple and sensitive screening method for the detection and identification of smokeless gunpowder organic components.

Journal Article↗
PubMed2003

Trace explosive detection in aqueous samples by solid-phase extraction ion mobility spectrometry (SPE-IMS).

Law enforcement agencies use ion mobility spectrometers for the detection of explosives, drugs of abuse, and chemical warfare agents. Ion mobility spectrometry (IMS) has the advantages of short analysis times, detections in the parts per billion concentrations, and high sensitivity. On-site environmental analysis of explosives or explosive residues in water is possible with ion mobility spectrometers. Unfortunately, the direct analysis of low levels of explosives in water is difficult. Extraction provides a method for pre-concentrating the analytes and removing interferents. Coupling solid-phase extraction (SPE) with IMS is useful for the identification of trace amounts of explosives in water. Commercially available SPE disks were used. After extraction, the sample disk is inserted into the ion mobility spectrometer, where the analytes are thermally desorbed from the disk. Concentrations as low as one part per trillion were detected with a Barringer Ionscan 350. An external computer and acquisition software (LabVIEW, National Instruments) were used to collect data. SIMPLISMA (SIMPLe-to-use-Interactive Self-modeling Mixture Analysis) was applied to the data to resolve features that vary with respect to time.

Aniline Compounds↗
PubMed2005

Determination of parabens in pharmaceutical formulations by solid-phase microextraction-ion mobility spectrometry.

Solid-phase microextraction (SPME) coupled with ion mobility spectrometry (IMS) was used for the detection and quantitation of 4-hydroxybenzoate preservatives, methylparaben, ethylparaben, propylparaben, and butylparaben, in commercial pharmaceutical products. For the first time, SPME-IMS is described for the simultaneous detection, separation, and quantitation of multiple analytes in complex matrixes. The parabens are extracted from the samples using SPME, and the analytes on the fiber are heated by the IMS desorber unit and vaporized into the drift tube. The four preservatives differing only by a methyl group were separated in less than 18 ms. The analytical procedure was optimized for fiber coating selection, extraction time, sample pH, sample volume, ionic strength, and IMS conditions. Separation characteristics such as resolution, theoretical plates, and drift times of the parabens were also evaluated based on the direct interfacing of SPME to IMS. The conditions were tested using six over-the-counter topical products containing various combinations of preservatives. Analysis of the samples by SPME-IMS using benzyl paraben as an internal standard yields good comparison to an HPLC method, thereby reinforcing the applicability of this technique as a method for routine analysis. Limits of detection were 10 ng/mL for methylparaben and ethylparaben and 5 ng/mL for propylparaben and butylparaben. Good linearity range and reproducibility of less than 8% were obtained.

Calibration↗
PubMed2006

High-resolution field asymmetric waveform ion mobility spectrometry using new planar geometry analyzers.

Field asymmetric waveform ion mobility spectrometry (FAIMS) has emerged as a powerful tool of broad utility for separation and characterization of gas-phase ions, especially in conjunction with mass spectrometry (MS). In FAIMS, ions are filtered by the dependence of mobility on electric field while being carried by gas flow through the analytical gap between two electrodes of either planar (p-) or cylindrical (c-) geometry. Most FAIMS/MS systems employ c-FAIMS because of its ease of coupling to MS, yet the merits of the two geometries have not been compared in detail. Here, a priori simulations reveal that reducing the FAIMS curvature always improves resolution at equal sensitivity. In particular, the resolving power of p-FAIMS exceeds that of c-FAIMS, typically by a factor of 2-4 depending on the ion species and carrier gas. We have constructed a new planar FAIMS incorporating a curtain plate interface for effective operation with an ESI ion source and joined to an MS using an ion funnel interface with a novel slit aperture. The resolution increases up to 4-fold over existing c-FAIMS, even though the analysis is approximately 2 times faster. This allows separation of species not feasible in previous FAIMS studies, e.g., protonated leucine and isoleucine or new bradykinin isomers. The improvement for protein conformers (of ubiquitin) is less significant, possibly because of multiple unresolved geometries.

Computer Simulation↗
PubMed2004

Correlation of mass spectrometry identified bacterial biomarkers from a fielded pyrolysis-gas chromatography-ion mobility spectrometry biodetector with the microbiological gram stain classification scheme.

A pyrolysis-gas chromatography-ion mobility spectrometry (Py-GC-IMS) briefcase system has been shown to detect and classify deliberately released bioaerosols in outdoor field scenarios. The bioaerosols included Gram-positive and Gram-negative bacteria, MS-2 coliphage virus, and ovalbumin protein species. However, the origin and structural identities of the pyrolysate peaks in the GC-IMS data space, their microbiological information content, and taxonomic importance with respect to biodetection have not been determined. The present work interrogates the identities of the peaks by inserting a time-of-flight mass spectrometry system in parallel with the IMS detector through a Tee connection in the GC module. Biological substances producing ion mobility peaks from the pyrolysis of microorganisms were identified by their GC retention time, matching of their electron ionization mass spectra with authentic standards, and the National Institutes for Standards and Technology mass spectral database. Strong signals from 2-pyridinecarboxamide were identified in Bacillus samples including Bacillus anthracis, and its origin was traced to the cell wall peptidoglycan macromolecule. 3-Hydroxymyristic acid is a component of lipopolysaccharides in the cell walls of Gram-negative organisms. The Gram-negative Escherichia coli organism showed significant amounts of 3-hydroxymyristic acid derivatives and degradation products in Py-GC-MS analyses. Some of the fatty acid derivatives were observed in very low abundance in the ion mobility spectra, and the higher boiling lipid species were absent. Evidence is presented that the Py-GC-ambient temperature and pressure-IMS system generates and detects bacterial biochemical information that can serve as components of a biological classification scheme directly correlated to the Gram stain reaction in microorganism taxonomy.

Biomarkers↗
PubMed2000

Investigation of bovine ubiquitin conformers separated by high-field asymmetric waveform ion mobility spectrometry: cross section measurements using energy-loss experiments with a triple quadrupole mass spectrometer.

High-field asymmetric waveform ion mobility spectrometry (FAIMS) was used to separate gas-phase conformers of bovine ubiquitin produced by electrospray ionization. These conformers were sampled by a triple quadrupole mass spectrometer where energy-loss experiments, following the work of Douglas and co-workers, were used to determine their cross sections. The measured cross sections for some conformers were readily altered by the voltages applied to the interface ion optics, therefore very gentle mass spectrometer interface conditions were required to preserve gas-phase conformers separated by FAIMS. Cross sections for 19 conformers (charge states +5 through +13) were measured. Two conformers for the +12 charge state, which were readily separated in FAIMS, were found to have similar cross sections. Based on a method to calibrate the collision gas thickness, the cross sections measured using the FAIMS/energy-loss method were compared with literature values determined using drift tube ion mobility spectrometry. The comparison illustrated that the conformers of bovine ubiquitin that were identified using drift tube ion mobility spectrometry were also observed using the FAIMS device.

Algorithms↗
PubMed2003

Thermal ionization ion mobility spectrometry of alkali salts.

Positive and negative thermal ionization ion mobility spectra (TI-IMS) of some sodium and potassium halides are reported here. The data provide the first measurement of the thermal ionization ion mobility spectrometry of inorganic compounds. A thin Nichrome filament was used as a thermionic ionization source. Sample was directly deposited on the filament, where it was heated and ionized. Each salt produced a different ion mobility pattern, but all sodium salts spectra were common in their first peak. This peak differs from the common peak observed in the spectra of potassium salts. The drift time of the second peak in all spectra was found to be linearly dependent on the size of the counteranion of the salt. Negative thermal ionization ion mobility spectra of alkali halides were also observed. An alkali halide salt (MX), in general, produced its own anion as well as some heavier ions that are thought to be hydrated X- (MX)n species. The capability of the method in quantitative analysis was demonstrated by measuring potassium impurity in sodium bromide. A detection limit of 0.01% K+ in NaBr and a linear rage of 3 orders of magnitude were obtained. The results from this study suggest that TI-IMS has potential as a field technique for the detection of some elements in samples.

Journal Article↗
PubMed1998

Detection of designer drugs in human hair by ion mobility spectrometry (IMS).

Since its inception in the early 1970s under the name plasma chromatography, ion mobility spectrometry (IMS) has undergone great changes. It is now utilized more and more in forensic science laboratories where it is used to detect explosives and environmental pollutants [1-4] as well as its use in detecting drugs of abuse [5-8]. Although IMS is known for nearly 30 years now [9], relatively few cases of the application of ion mobility spectrometry to the analysis of human hair have been reported [10-12]. The authors report a new and quick method to rapidly screen and determine MDMA ('ecstasy', 'Adam') and MDEA ('Eve') in human hair. The proposed method using trihexylamine as internal standard resulted in a rapid procedure useful in screening human hair specimens for designer drugs.

3,4-Methylenedioxyamphetamine↗
PubMed2004

Separation of beta2-microglobulin conformers by high-field asymmetric waveform ion mobility spectrometry (FAIMS) coupled to electrospray ionisation mass spectrometry.

An investigation into the use of high-field asymmetric waveform ion mobility spectrometry (FAIMS) coupled to electrospray ionisation mass spectrometry (ESI-MS) for the differentiation of co-populated protein conformers has been conducted on the amyloidogenic protein beta(2)-microglobulin (beta(2)m). Accumulation of beta(2)m in vivo can result in the deposition of insoluble fibrils whose formation is thought to originate from partially folded protein conformers; hence, the folding properties of beta(2)m are of significant interest. We have analysed beta(2)m using ESI-FAIMS-MS under a range of pH conditions and have studied the effect of the ion mobility spectrometry parameters on the behaviour of the various protein conformers. The data show that different protein conformers can be detected and analysed by ESI-FAIMS-MS, the results being consistent with observations of pH denaturation obtained using complementary biophysical techniques. A variant of beta(2)m with different folding characteristics has been analysed for comparison, and the distinctions observed in the data sets for the two proteins are consistent with their folding behaviour. ESI-FAIMS-MS offers significant opportunities for the study of the conformational properties of proteins and thus may present valuable insights into the roles that different conformers play in diseases related to protein folding.

Amino Acid Sequence↗
PubMed2003

Characterization of naphthenic acids by electrospray ionization high-field asymmetric waveform ion mobility spectrometry mass spectrometry.

Electrospray ionization (ESI) high-field asymmetric waveform ion mobility spectrometry (FAIMS) was combined with quadrupole, time-of-flight, and tandem mass spectrometry to characterize commercial and naturally occurring naphthenic acids (NA) mixtures. This new method provides quantitatively reliable mass and isomer distributions of NA components in approximately 3 min without extensive sample preparation. ESI-FAIMS-MS seems to be especially useful for characterization of fragile ions that cannot be detected by other methods. A unique part of this technique is separation of structural isomers that proved to be critical in determination of elemental composition and in structure elucidation. Tandem mass spectrometry of NA ions separated by FAIMS provides more information about the structure of NA than other methods in the field of NA analysis.

Journal Article↗
PubMed2005

Solid phase micro-extraction coupled with ion mobility spectrometry for the analysis of ephedrine in urine.

Quantitative solid phase micro-extraction (SPME) coupled with ion mobility spectrometry is demonstrated using the analysis of ephedrine in urine. Since its inception in the 1970's ion mobility spectrometry (IMS) has evolved into a useful technique for laboratories to detect explosives, chemical warfare agents, environment pollutants and, increasingly, for detecting drugs of abuse. Ephedrine is extracted directly from urine samples using SPME and the analyte on the fiber is heated by the IMS desorber unit and vaporized into the drift tube. The analytical procedure was optimized for fiber coating selection, extraction temperature, extraction time, sample pH, and analyte desorption temperature. The carryover effects, ion fragmentation characteristics, peak shapes, and drift times of ephedrine were also evaluated based on the direct interfacing of SPME to IMS. A limit of detection of 50 ng/mL of ephedrine in urine and a linear range of 3 orders of magnitude were obtained, showing that SPME-IMS compares well to other techniques for ephedrine and drug analysis presented in the literature.

Central Nervous System Stimulants↗