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Conformers of equine cytochrome c were investigated in the gas phase using a combination of high-field asymmetric waveform ion mobility spectrometry (FAIMS) and hydrogen-deuterium (H-D) exchange. Electrospray generated ions of equine cytochrome c were exposed to a low concentration of [D.sub.2]O vapour while being transported by a flow of nitrogen through a FAIMS device. During this transport period of about 250 ms in the FAIMS analyzer, the various conformers of multiply charged ions of cytochrome c were simultaneously undergoing H-D exchange and being separated from each other. The extent of H-D exchange was calculated from the observed m/z of conformers after exposure to [D.sub.2]O vapour in FAIMS. The complementary nature of these two methods resulted in observations supporting a greater number of conformers (e.g., at least 11 conformers were identified for the +16 charge state) than would be expected by analyzing the FAIMS data and the H-D exchange data independently. Key words: FAIMS, H-D exchange, mass spectrometry, protein conformations, electrospray ionization. On a Etudie les conformeres du cytochrome c equin en phase gazeuse en utilisant une combinaison d'Echange d'hydrogene et de deuterium et de spectrometrie de la mobilite ionique, de forme d'onde asymetrique et a haut champ (<< FAIMS >>). Les ions generes par electronebulisation du cytochrome c equin sont exposes a une faible concentration de vapeur de [D.sub.2]O pendant qu'ils sont entraines par un courant d'azote a travers un analyseur FAIMS. Au cours de la periode de 250 ms de ce transport dans l'analyseur FAIMS, les divers conformeres des ions du cytochrome c a charges multiples subissent des echanges H-D simultanes et se separent les uns des autres. On a calcule le degre d'echange H-D a partir des valeurs m/z observees pour les conformeres apres leur exposition 5 la vapeur de [D.sub.2]O dans l'analyseur FAIMS. La nature complementaire de ces deux methodes permet de faire des observations qui suggerent l'existence d'un beaucoup plus grand nombre de conformeres (par exemple, on a identifie au moins 11 conformeres pour l'etat de charge +16) que le nombre attendu sur la base d'une analyse des donnees FAIMS et des donnees d'echange H-D prises independamment. Mots cles : << FAIMS >>, echange H-D, spectrometrie de masse, conformations de proteines, ionisation par electronebulisation. [Traduit par la Redaction], Introduction The ability to produce intact ions from large molecules (1, 2) has led to the development of several methods for studying biomolecular ions in the gas phase (3, 4). [...]

Amphetamine, methamphetamine, and their methylenedioxy derivatives have been identified and measured in a human urine matrix using solid-phase microextraction (SPME) and high-field asymmetric waveform ion mobility spectrometry (FAIMS) in combination with electrospray ionization (ESI) and mass spectrometric detection (MS). Limits of detection in human urine between 200 pg/mL and 7.5 ng/mL have been achieved. The use of a simple extraction method, SPME, combined with the high sensitivity and selectivity of ESI-FAIMS-MS eliminates the need for chromatographic separation and allows for very rapid sample processing.

Improvements to the FAPES - mass spectrometer interface permit high-sensitivity elemental analysis with the FAPIMS ion source. The source is configured with an integrated contact cuvette in which a 40-MHz He plasma is sustained at atmospheric pressure. A differentially pumped interface consisting of a modified sampler cone (0.45-mm i.d.) and tandem skimmer cone (0.88-mm i.d.) serve to sample the plasma from the open end of the cuvette. Mass spectra, characterizing plasma species with the furnace at elevated temperatures, show He(sub 2)(super +), C(super +), N(super +), O(super +), NH(sub 4)(super +), H(sub 3)O(super +), N(sub 2)(super +), and O(sub 2)(super +) and carbonaceous ions. Transient ion signals, generated during the atomization of a number of analytes introduced in solution form, reveal that the plasma contains sufficiently energetic species to ionize and determine elements having ionization potentials as high as 9.75 eV (Se). Figures of merit, including the estimated absolute limits of detection, measurement precision, isotope ratio measurements, and linear dynamic range, are discussed. In general, the measurement precision is approximately 5% and the absolute limits of detection range from 20 to 500 fg for Mg, Fe, Co, Cu, Se, Cd, Cs, and Pb.

The lower limit of detection for low molecular weight polar and ionic analytes using electrospray ionization-mass spectrometry (ESI-MS) is often severely compromised by an intense background that obscures ions of trace components in solution. Recently, a new technique, referred to as high-field asymmetric waveform ion mobility spectrometry (FAIMS), has been shown to separate gas-phase ions at atmospheric pressure and room temperature. A FAIMS instrument is an ion filter that may be tuned, by control of electrical voltages, to continuously transmit selected ions from a complex mixture. This capability offers significant advantages when FAIMS is coupled with ESI, a source that generates a wide variety of ions, including solvent clusters and salt adducts. In this report, the tandem arrangement of ESI-FAIMS-MS is used for the analysis of haloacetic acids, a class of disinfection byproducts regulated by the US EPA. FAIMS is shown to effectively discriminate against background ions resulting from the electrospray of tap water solutions containing the haloacetic acids. Consequently, mass spectra are simplified, the selectivity of the method is improved, and the limits of detection are lowered compared with conventional ESI-MS. The detection limits of ESI-FAIMS-MS for six haloacetic acids ranged between 0.5 and 4 ng/mL in 9:1 methanol/tap water (5 and 40 ng/mL in the original tap water samples) with no preconcentration, derivatization, or chromatographic separation prior to analysis.

A commercially available ion mobility spectrometer was interfaced to a custom-built linear time-of-flight (TOF) mass spectrometer for the purpose of examining electrospray-generated plumes. Ionic species that were separated in the ion mobility spectrometer could be selectively determined with the TOF mass spectrometer. Tetraalkylammonium salts, a peptide, and proteins were examined. Their ion mobility spectra typically comprised a few peaks; some of these mobility-resolved species produced characteristic electrospray ions, while others of lower relative mobility did not. The TOF mass spectra of cytochrome c, injected from the ion mobility spectrometer at an indicated temperature of 90 [degrees] C or lower, showed signs that were characteristic of protein-solvent clustering.

The electrospray mass spectra of basic protein solutions containing ketones exhibit ions that are attributable to protein-ketone adducts whose relative abundances are in accordance with the relative concentrations of these adducts in solution. In a basic solution, the deprotonated (neutral) amino groups in a protein may be alkylated by ketone molecules to form Schiff bases. The extent of alkylation may be approximated by statistics if the reactivity of each amino group is identical. The relative ion abundances of these adducts have been found to follow their statistical distributions expected in solution. The reaction to form Schiff bases may be applied to the measurement of the number of primary amino sites (N-terminus plus lysine residues) in a protein. Excellent agreement with known numbers was observed for all 18 proteins measured.

Liquid chromatography can be used to give chemistry students a real-world problem to work on with the determination of paralytic shellfish poisons in shellfish meat from infested beaches. Students can determine saxitoxin concentrations which, when greater than 1 mg, can be fatal for humans. Procedures for harvesting shellfish, extracting the toxin and analyzing the extract using liquid chromatography are included.

The continuous gas-phase ion separation and atmospheric pressure focusing properties of high-field asymmetric waveform ion mobility spectrometry (FAIMS) offer significant advantages for the mass spectrometric analysis of tryptic digests of proteins. In this study, tryptic peptides of pig hemoglobin were examined by ESI-FAIMS-MS using a newly designed FAIMS device. The new, hemispherical geometry of the inner electrode served to deliver the ions, via the gas flows, to the center axis of the FAIMS analyzer, improving the sensitivity relative to previous prototypes. Mass spectra collected using this new FAIMS showed significantly less chemical background noise than conventional ESI-MS, while maintaining approximately the same absolute sensitivity as that observed with ESI-MS. As a consequence of the ion separation in FAIMS, the identification of the tryptic fragments was simplified and some peptides, such as the triply protonated [VVAGVANALAHK.sup.3+], that were obscured by the intense background of ESI-MS, were readily detected using ESI-FAIMS-MS. In addition, the FAIMS device was shown to separate isobaric ions at m/z 532.4. Correlations between CV and mass-to-charge ratio, as well as CV and ionic collision cross section, were evaluated for 38 peptide ions identified in the tryptic digest. The correlation between the CV of the peptide and the mass-to-charge ratio is very poor, indicating good orthogonality between the separation by FAIMS and the separation by mass spectrometry.

A combination of electrospray ionization, high-field asymmetric waveform ion mobility spectrometry, and mass spectrometry (ESI-FAIMS-MS) was used for the analysis of a solution containing a mixture of the nine chlorinated and brominated haloacetic acids. For a carrier gas of nitrogen in the FAIMS analyzer, haloacetate anions of the mono- and dihalogenated acids and the decarboxylated anions of three of the trihalogenated acids were detected. No signal was observed for bromodichloroacetic acid (BDCAA) at a dispersion voltage of -3400 V. The addition of a small amount of carbon dioxide to the nitrogen carrier gas resulted in the detection of the pseudomolecular trihaloacetate anions, including [BDCA.sup.-], and significant increases in sensitivities for the trihalogenated species. The addition of carbon dioxide to the nitrogen carrier gas had little effect on the mono- and dihalogenated anions. Quantitative analysis of the nine haloacetic acids, using flow injection, gave detection limits between 5 and 36 parts-per-trillion in 9/1 methanol/water (v/v) containing 0.2 mM ammonium acetate.

High-valent nitrido and amido complexes of ruthenium, osmium and chromium were investigated by electrospray tandem mass spectrometry. The results showed the molecular ion as the base peak with a minimal degree of fragmentation. The collision-induced dissociation of these complexes have been explained in terms of the intrinsic metal-ligand bond strengths.

High-field asymmetric waveform ion mobility spectrometry (FAIMS) is a new technique that separates gas-phase ions at atmospheric pressure (760 Tort) and room temperature. A FAIMS instrument acts as an ion filter and can be set to continuously transmit one type of ion. Despite the stringent requirement for a flow of clean, dry gas in the FAIMS analyzer region, a method of coupling electrospray to FAIMS has been developed. The identity of the electrospray ions separated by FAIMS was determined using mass spectrometry (FAIMS-MS). The theory of FAIMS is discussed, and electrospray FAIMS-MS spectra of several compounds in modes P1, P2, N1, and N2 are presented. Ions appearing in P1 and N1 modes tend to have mobilities that increase as a function of increasing electric field strength, whereas ions appearing in P2 and N2 modes tend to have mobilities that decrease. In general, low-mass ions are focused in P1 and N1 modes, whereas larger ions (e.g., proteins) are focused in P2 and N2 modes. Short-chain peptides, [(Gly).sub.n] where n = 1-6, are shown to cross over from P1 mode into P2 mode as the chain length increases. The removal of the low-mass solvent cluster ions, combined with a reduction of the background noise in electrospray FAIMS-MS, results in an improved signal-to-noise ratio for mass spectra of larger ions (e.g., cyctochrome c) when compared with conventional electrospray-MS. Preliminary results also suggest that various charge states of cytochrome c can be distinguished by FAIMS, implying that the ion mobility of these species at high electric field strength is sensitive to the structure of the protein ion. The linearity of response of electrospray FAIMS-MS was investigated using leucine enkephalin and shows the calibration curve to be linear for [approximately]3 orders of magnitude.

Investigates the focusing of ions at atmospheric pressure and room temperature in a high-field asymmetric waveform ion mobility spectrometer (FAIMS). Principle of operation of FAIMS; Dependence of sensitivity on the dispersion voltage; Modeling of the ion motion in the FAIMS; Theory of ion focusing in FAIMS.

Presents a mass spectrometric characterization of a high-field asymmetric waveform ion mobility spectrometer (IMS). Applications of IMS; Difference from the high-field asymmetric waveform IMS; Factors affecting the sensitivity and peak locations in the voltage spectra.

The mechanism of the collision-induced fragmentation of peracetylated methyl-α-D-glucopyranoside was investigated using deuterium-labelled acetates and sequential mass spectrometry. Loss of the substituent at C(1), the anomeric carbon, yields an ion of m/z 331, [C14H19O9]+. This ion further dissociates via two pathways, the first including m/z 271, [C12H15O7]+, 169, [C8H9O4]+ and 109, [C6H5O2]+, and the second including m/z 211, [C10H11O5]+, 169, [C8H9O4]+ and 127 [C6H7O3]+. The first path proceeds via loss of acetate at C(3), followed by a single-step concerted loss of acetates from C(2) and C(4), and ending with loss of acetate from C(6). The second path proceeds predominantly via loss of acetates from C(3) and C(4), elimination of ketene from the C(2)-acetate and finally loss of ketene from the acetate at C(6). This path is also characterized by an ill-defined series of parallel decomposition reactions involving acetates from other sites on the molecule. At low collision energy, and in the absence of collision gas (unimolecular reaction conditions), the former pathway predominates; m/z 331 dissociates via loss of acetate at C(3), followed by a single-step concerted loss of acetates from C(2) and C(4). [ABSTRACT FROM AUTHOR]

Careful analysis is made of the accuracies possible when gaseous ion mobilities are determined from data obtained by combining electrospray ionization (ESI), high-field asymmetric waveform ion mobility spectrometry (FAIMS) at atmospheric pressure and room temperature, and mass spectrometry (MS). New results are reported for the mobilities of positive and negative amino acid ions in air at elevated values of E/N, the ratio of the electric field strength to the gas number density. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Approaches to separation and characterization of ions based on their mobilities in gases date back to the 1960s. Conventional ion mobility spectrometry (IMS) measures the absolute mobility, and field asymmetric waveform IMS (FAIMS) exploits the difference between mobilities at high and low electric fields. However, in all previous IMS and FAIMS experiments ions experienced an essentially free rotation; thus the separation was based on the orientationally averaged cross-sections Omega(avg) between ions and buffer gas molecules. Virtually all large ions are permanent electric dipoles that will be oriented by a sufficiently strong electric field. Under typical FAIMS conditions this will occur for dipole moments >400 D, found for many macroions including most proteins above approximately 30 kDa. Mobilities of aligned dipoles depend on directional cross-sections Omega(dir) (rather than Omega(avg)), which should have a major effect on FAIMS separation parameters. Here we report the FAIMS behavior of electrospray-ionization-generated ions for 10 proteins up to approximately 70 kDa. Those above 29 kDa exhibit a strong increase of mobility at high field, which is consistent with predicted ion dipole alignment. This effect expands the useful FAIMS separation power by an order of magnitude, allowing separation of up to approximately 10(2) distinct protein conformers and potentially revealing information about Omega(dir) and ion dipole moment that is of utility for structural characterization. Possible approaches to extending dipole alignment to smaller ions are discussed.