A challenging aspect of structural elucidation of carbohydrates is gaining unambiguous information for anomers, linkage, and position isomers. Such isomers with identical mass can't be easily distinguished in mass spectrometry and a separation step is required prior to mass spectrometry identification. In our laboratory, gas-phase separation and differentiation of anomers, linkage, and position isomers of disaccharides was achieved using High-Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS). The FAIMS method responds to changes in ion mobility at high field rather than absolute values of ion mobility, and was shown to provide efficient separation and identification of disaccharide isomers at high sensitivity. Separation of analyzed disaccharide isomers can be accomplished at low nM level in a matter of seconds without sample purification or fractionation. Capability for examining a large population of ionic species of disaccharides by this method allowed for correlating structural details of disaccharide isomers with their separation properties in FAIMS. Results for disaccharide isomers indicate that this method could be applied to a larger group of carbohydrates. ( Mass spectrometry has shown a unique ability to resolve certain structural ambiguities. Permethylation is a well developed but time-consuming GC-MS method in linkage analysis of oligosaccharides [1,2]. Other methods implementing the derivatization of saccharides have been used to obtain their structural information [3][4][5][6][7][8][9][10][11]. The soft mass spectrometry ionization techniques such as fast atom bombardment (FAB) [12][13][14][15][16], liquid secondary ionization mass spectrometry (LSIMS) [17,18], along with matrix-assisted laser desorption ionization (MALDI) [19 -23], and electrospray ionization (ESI) [24 -28] have gained attention as approaches to investigate underivatized oligosaccharides. Collision-induced dissociation (CID) offers the possibility to assign details of carbohydrate structure such as sugar sequence for linear oligosaccharides [12], linkage position [12,[15][16][17]29], and differentiation of anomers [25,30]. In addition to analyzing protonated or deprotonated molecular ions of saccharides in CID, alkali metal adduct ions have been used to promote fragmentation of ligand-carbohydrate complexes. In the positive ion mode, calcium and magnesium adducts of oligosaccharides were investigated for the elucidation of the linkage position of trisaccharides [26] and cobalt complexes have been used to differentiate the anomeric configuration of disaccharides [30]. In the negative ion mode, decomposition of chloride adducts was investigated for differentiation of the linkage position of disaccharides [31].Despite recent advances in tandem mass spectrometry of carbohydrates, the spectral differences for some isomers are very small and they do not provide unambiguous identification. This is especially true when a mixture of isomers with the same m/z has to be analyzed. In such applications a separation step is required ...

Direct radical addition reactions at the C(8)-site of 2'-deoxyguanosine (dG) can afford C(8)-Ar-dG adducts that are produced by carcinogenic arylhydrazines, polycyclic aromatic hydrocarbons, and certain phenolic toxins. Such modified nucleobases are also highly fluorescent for sensing applications and possess useful electron transfer properties. The site-specific synthesis of oligonucleotides containing the C(8)-Ar-G adduct can be problematic. These lesions are sensitive to acids and oxidants that are commonly used in solid-phase DNA synthesis and are too bulky to be accepted as substrates for enzymatic synthesis by DNA polymerases. Using the Suzuki-Miyaura cross-coupling reaction, we have synthesized a number of C(8)-Ar-G-modified oligonucleotides (dimers, trimers, decamers, and a 15-mer) using a range of arylboronic acids. Good to excellent yields were obtained, and the reaction is insensitive to the nature of the bases flanking the convertible 8-Br-G nucleobase, as both pyrimidines and purines are tolerated. The impact of the C(8)-Ar-G lesion was also characterized by electrospray ionization tandem mass spectrometry, UV melting temperature analysis, circular dichroism, and fluorescence spectroscopy. The C(8)-Ar-G-modified oligonucleotides are expected to be useful substrates for diagnostic applications and understanding the biological impact of the C(8)-Ar-G lesion.

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.

Drinking water is a complex mixture that contains thousands of naturally occurring and anthropogenic contaminants. Liquid chromatography-mass spectrometry (LC-MS) methods have gained a tremendous popularity in monitoring nonvolatile, highly polar, and thermally labile components in drinking water. It is well recognized, however, that there are difficulties or limitations of LC-MS methods associated with (1) significant resources (time and effort) involved in sample preparation (preconcentration, fractionation, separation), (2) low screening capacity for target contaminants, and (3) insufficient capabilities for structural identification (elucidation) of nontarget contaminants. Consequently, LC-MS methods are mainly used for the detection of target contaminants (compounds identified in drinking water before), seldom for the structural identification of abundant nontarget pollutants (unidentified pollutants in drinking water), and almost never for the structural identification of nontarget components at a trace level. The paper presents a new method of electrospray ionization high field asymmetric waveform ion mobility spectrometry mass spectrometry (ESI-FAIMS-MS), which can detect a large number of water pollutants in a quick and convenient fashion without preconcentration, fractionation, derivatization, or column separation. Most importantly, the method provides structural identification of nontarget contaminants including species present in drinking water at a sub-parts-per-billion concentration level. The identification of previously unknown contaminants was based on mass measurements of investigated ions and their fragments in mass and tandem mass spectrometry. Elemental compositions of these ions, determined by mass measurements, were used to link dissociation patterns of investigated species with their chemical structures. Characterization of nontarget contaminants of chlorine-treated drinking water by ESI-FAIMS-MS has revealed many previously unknown disinfection byproducts. The most intriguing compound, from a group of highly polar hydroxycarboxylic acids discovered in the study, was the most abundant component of drinking water, glycolic acid. Glycolic acid (toxic to kidneys and associated with a moderate maternal toxicity) has never been considered as a drinking water contaminant, despite the fact that it is present in drinking water at a higher concentration (high ppm) than concentrations of highly polar water pollutants that had attracted most attention in the past. The process of structural elucidation of discovered pollutants, including ultratrace contaminants representing a variety of carboxylic acids, will be presented in detail. The structural identification of highly polar contaminants in drinking water presented in the paper is rarely reported in the literature. The key experimental feature of the ESI-FAIMS-MS method is FAIMS separation, which significantly improves the identification capabilities of mass spectrometry.

Articles you may be interested inAn integrated ion trap and time-of-flight mass spectrometer for chemical and photo-reaction dynamics studies Rev. Sci. Instrum. 83, 043103 (2012); 10.1063/1.3700216 Hybrid quadrupole mass filter/quadrupole ion trap/time-of-flight-mass spectrometer for infrared multiple photon dissociation spectroscopy of mass-selected ions Rev. Sci. Instrum. 82, 054101 (2011); 10.1063/1.3585982 Multiple-ion-beam time-of-flight mass spectrometer Rev. Sci. Instrum. 72, 3386 (2001); 10.1063/1.1380682 On the combination of a linear field free trap with a time-of-flight mass spectrometer Rev. Sci. Instrum. 72, 2900 (2001); 10.1063/1.1373666The effect of using silicon based diffusion pump fluid on spectral quality in an electrospray ionization ion trap/time-of-flight mass spectrometer Rev.Laser photo-induced dissociation ͑PID͒ is an attractive alternative to collision-induced dissociation ͑CID͒ in probing structural features of biomolecules, such as peptides, by mass spectrometry. We report a new experimental setup for PID studies of biomolecules. It involves the use of an ion trap/time-of-flight mass spectrometer for the detection of PID products. The intact molecular ions are produced by electrospray ionization and introduced into a quadrupole ion trap. The ions stored in the trap are then dissociated by using a 266 nm laser beam from a pulsed Nd:yttriumaluminium-garnet laser. After a short delay, all the fragment ions are extracted out of the trap and mass analyzed by a linear time-of-flight ͑TOF͒ mass spectrometer. The applications of this instrument for the PID studies of several peptides are demonstrated. The PID spectra are compared to those obtained by CID in the same instrument. It is shown that the amount of photoenergy deposited for fragmentation can be controlled by laser absorption property of the ions, laser power, number of laser pulses, and ion trap buffer gas pressure. Energetically optimal PID process results in spectra providing structural information similar to that obtained from CID. An excessive amount of photoenergy deposited to the fragmenting ions favors the formation of deep fragmentation products at the cost of sequence related ions. It is demonstrated that in some cases the PID technique has the potential in probing structural features of peptides that cannot be fragmented in ion trap CID. Finally, it is shown that the combination of the ion trap with the TOF detector provides a unique capability for fast detection of ions formed via PID. The PID products generated after a time delay from 1.5 s to several milliseconds following the dissociation laser pulse can be characterized.