This review article compares and contrasts various types of ion mobility-mass spectrometers available today and describes their advantages for application to a wide range of analytes. Ion mobility spectrometry (IMS), when coupled with mass spectrometry, offers value-added data not possible from mass spectra alone. Separation of isomers, isobars, and conformers; reduction of chemical noise; and measurement of ion size are possible with the addition of ion mobility cells to mass spectrometers. In addition, structurally similar ions and ions of the same charge state can be separated into families of ions which appear along a unique mass-mobility correlation line. This review describes the four methods of ion mobility separation currently used with mass spectrometry. They are (1) drift-time ion mobility spectrometry (DTIMS), (2) aspiration ion mobility spectrometry (AIMS), (3) differential-mobility spectrometry (DMS) which is also called field-asymmetric waveform ion mobility spectrometry (FAIMS) and (4) traveling-wave ion mobility spectrometry (TWIMS). DTIMS provides the highest IMS resolving power and is the only IMS method which can directly measure collision cross-sections. AIMS is a low resolution mobility separation method but can monitor ions in a continuous manner. DMS and FAIMS offer continuous-ion monitoring capability as well as orthogonal ion mobility separation in which high-separation selectivity can be achieved. TWIMS is a novel method of IMS with a low resolving power but has good sensitivity and is well intergrated into a commercial mass spectrometer. One hundred and sixty references on ion mobility-mass spectrometry (IMMS) are provided.

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This manuscript 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 (IMS), 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-α-glucopyranoside, glucose, penicillamine, valinol, phenylalanine, and tryptophan from their respective racemic mixtures.

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. In order to fully characterize oligosaccharides derived from biological sources, a number distinct of challenges must be over come. These issues arise primarily from the existence of biological oligosaccharides as sets of isomers. A number of approaches to address isomeric carbohydrate structures using mass spectrometry have been reported. These methods include periodate oxidation/borohydride reduction, followed by hydroxyl methylation or peracetylation [9, 10], derivatization of monosaccharides or short oligosaccharides with amines such as diethylenetriamine at the reducing end followed by metal complexation [11,12], or prediction of possible fragmentation pathways after permethylation [13]. Although modern mass spectrometry is an exquisite tool in itself for the separation of molecules having different m/z values, it cannot rule out the possibility that mass spectra derived from selected precursor ions are not derived from an isobaric mixture. And to complicate matters even further, it is entirely possible that the fragment ions themselves are isobars. On a fundamental level, the stereochemistry of monosaccharides, as product ions derived from a larger molecule, cannot be unambiguously established from a fragmentation pattern. Aldohexoses, for example, come in sixteen different stereochemical variants, and fragmentation data that would uniquely differentiate each of them has yet to be convincingly furnished, particularly where they are derived as product ions from larger molecules. To address the stereochemical blindness of mass spectrometry, product ions must first be separated based upon a physical principle that is not dependent upon m/z prior to fragmentation.Traditional chromatographic methods, most notably liquid and gas, have been used to provide an additional