Isomeric distinction of small oligosaccharides: a bottom-up approach using the kinetic method

Rapid discrimination and quantification of isomeric flavonoid-O-diglycosides in Citrus paradisi cv. changshanhuyou by online extraction-quadrupole time-of flight tandem mass spectrometry

Rapid differentiation, characterization and quantification of isomers from complex mixtures by direct mass spectrometry (MS) remained an analytical challenge due to their similar or identical MS/MS spectra and matrix interferences. Here, we reported a novel online extraction-quadrupole time-of-flight tandem mass spectrometry (OLE-QTOF-MS/MS) system to rapid, efficient and sensitive analysis of interglycosidic linkage isomers (hesperidin and neohesperidin) in Citrus paradisi cv. Changshanhuyou (Changshanhuyou). OLE system packed with solid Changshanhuyou (0.02 mg) could be firstly used to online remove interferences with large polarities, and then online extract and enrich hesperidin and neohesperidin, which shows great potential to diminish the analysis time of sample pretreatment, as well as to reduce matrix effects and instrument consumption. Detailed fragmentation analysis found that, under positive ion mode, relative abundance of specific fragment ions m/z 449 to m/z 303 showed linear correlation to the mass content of hesperidin (0% to 100%) with good correlation coefficient (R² = 0.9958). Utilizing this method, the mass ratio of hesperidin to neohesperidin in Changshanhuyou was relatively quantified as 3.7:96.3 with RSD at 2.9%. Finally, using internal standard method, the absolute quantitative analysis was performed with acceptable reproducibility (RSD 1.3 and 4.5% for intra- and inter-day variations) and recoveries (from 95.9% to 108.9%), acceptable limit of detection (0.33 ng). In general, OLE-QTOF-MS/MS represented a promising and practical method for simple, rapid and effective analysis of isomeric compounds in complex matrices.

Identifying the D-Pentoses Using Water Adduction to Lithium Cationized Molecule

A method has been developed that is capable of distinguishing an exhaustive list of underivatized D-pentoses with only a mass spectrometer. Electrospray ionization (ESI) of a solution containing a pentose and a lithium salt yields [Pentose + Li]⁺. These lithiated pentoses adduct water in a quadrupole ion trap. The reaction rate of water adduction is unique for several of the pentose isomers. Additionally, there are multiple potential gas-phase lithiation sites to form [Pentose + Li]⁺. A mixture of ions with at least one reactive (water adducting) and at least one unreactive (non-adducting) lithiation site is formed for each pentose. The water adduction reaction rate along with the unreactive fraction of lithiated pentose can be used to completely discriminate all D-pentoses. Graphical Abstract ᅟ.

Multidimensional Analysis of 16 Glucose Isomers by Ion Mobility Spectrometry

Diastereomeric adducts comprising an enantiomerically pure monosaccharide analyte, a peptide, and/or an amino acid and a divalent metal ion (for 16 different monosaccharide isomers) are generated by electrospray ionization and analyzed by combined ion mobility spectrometry-mass spectrometry (IMS-MS) techniques. Mobility distributions of [l-Ser + M + H](+) (where l-Ser is l-serine and M is a given monosaccharide), [l-Phe-Gly + M + H](+) (where l-Phe-Gly is l-phenylalanine-glycine), and [Mn(II) + (l-Phe-Gly - H) + M](+) complex ions are used to determine collision cross sections (ccs in Å(2)), and groups of cross sections for different clusters are proposed as means of identifying the sugar isomers. Within one type of complex, variations in ccs do not always allow delineation between the 16 glucose isomers, but interestingly, when ccs of three different ions are combined as a spatial vector, enantiomers are partially resolved. As a result of this analysis, l-glucose, d-glucose, l-allose, d-allose, d-gulose, d-galactose, and l-mannose are delineated, and for all eight enantiomeric pairs, d and l entities display different coordinates. In addition, different combinations of amino acids, peptide, and metal ions are surveyed, and the potential for yielding unique coordinates for the generated diastereomeric complexes is assessed.

Complete hexose isomer identification with mass spectrometry

The first analytical method is presented for the identification and absolute configuration determination of all 24 aldohexose and 2-ketohexose isomers, including the D and L enantiomers for allose, altrose, galactose, glucose, gulose, idose, mannose, talose, fructose, psicose, sorbose, and tagatose. Two unique fixed ligand kinetic method combinations were discovered to create significant enough energetic differences to achieve chiral discrimination among all 24 hexoses. Each of these 24 hexoses yields unique ratios of a specific pair of fragment ions that allows for simultaneous determination of identification and absolute configuration. This mass spectrometric-based methodology can be readily employed for accurate identification of any isolated monosaccharide from an unknown biological source. This work provides a key step towards the goal of complete de novo carbohydrate analysis.

Differentiation of glucose-containing disaccharides isomers by fragmentation of the deprotonated non-covalent dimers using negative electrospray ionization tandem mass spectrometry

In this work, the glucose-containing disaccharide isomers were studied using negative electrospray ionization tandem mass spectrometry (ESI-MS/MS). Interestingly, the full-scan mass spectra of the disaccharides revealed that the deprotonated dimers were the predominant gas phase ions during ionization process. Importantly, several diagnostic fragment ions relative to linkage positions and anomeric configurations, arising from the covalent bond dissociation of dimers without breakdown of the non-covalent complexes, can be detected in the tandem mass spectra. Based on the scarce fragmentation characteristic, an original and simple approach for structural discrimination of disaccharide isomers was put forward. In addition, density functional theory (DFT) was employed to find out the reason why several fragmentations of intramolecular sugar bonds had preceded breakdown of the non-covalent complexes.

Identification of isomeric disaccharides in mixture by the 1-phenyl-3-methyl-5-pyrazolone labeling technique in conjunction with electrospray ionization tandem mass spectrometry

1-Phenyl-3-methyl-5-pyrazolone (PMP) labeling technique has hitherto proved to be a convenient and sensitive method for separating and detecting oligosaccharides. However, the detailed fragmentation of the derivatives by tandem mass spectrometry has been reported limitedly and no characteristic fragment ions for isomers have been detected. In this study, eight disaccharide isomers were labeled with PMP and analyzed by positive ion electrospray ionization multi-stage tandem mass spectrometry (ESI-MS(n)). In comparison with the native disaccharides, PMP labeled disaccharides gave rise to more fragment ions in the tandem mass spectra. The distinctive diagnostic fragment ions formed from cleavage of C-C bonds have been detected in the fragmentation of PMP-labeled disaccharide linkage isomers, allowing unambiguous assignment of the position of the glycosidic linkages. This feature is particularly useful for the structural determination of unknown isomeric disaccharides mixed together. In addition, the anomeric configurations can also be easily assigned based on the relative abundance ratios of the selected ion pairs. To verify the feasibility of the method used in the analysis of natural product, water soluble Panax Ginseng extract has been further investigated to identify its unknown disaccharides. The results confirmed that the PMP labeling technique in conjunction with ESI-MS(n) could offer a powerful and convenient tool for differentiation of structurally closely related isomers, even the unknown mixtures of isomeric disaccharides with different linkage types.