title: Negative matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectrometry fragmentation of synthetic analogs of the O-specific polysaccharide of Vibrio cholerae O:1 in the presence of anionic dopants.
abstract: Oligosaccharides (tri- to hexamers) that represent terminal epitopes of O-antigens of Vibrio cholerae O:1, serotypes Ogawa and Inaba, have been studied by negative matrix-assisted laser desorption/ionization time of flight/time-of-flight mass spectrometry (MALDI ToF/ToF MS). The [M - H(+)](-) ions are formed after expulsion of a proton from molecules studied under condition of MALDI MS analysis in the negative mode. Several ammonium salts (chloride, nitrate, hydrogencarbonate and hydrogensulfate) were used as additives to increase the formation of negative ions from saccharides. The most efficient was the addition of ammonium hydrogencarbonate, which increased the amount of [M - H(+)](-) ions more than six times. Between three fragmentation pathways, the new conjugated transfer of electrons within the second downstream unit of oligosaccharides was discovered. Production of these ions, which has not been observed in any other kinds of measurement, distinguishes substances belonging to Ogawa and Inaba serotypes. The negative MALDI ToF/ToF mass spectra are simpler and, at the same time, more informative, as compared with positive and negative electrospray ionization ion trap as well as with positive MALDI ToF/ToF analysis.
authors.affiliation: Institute of Analytical Chemistry, Academy of Sciences of the Czech Republic, Veverí 97, 611 42 Brno, Czech Republic.
authors.forename: Josef
authors.initials: J
authors.lastname: Chmelík
authors.forename: Pavel
authors.initials: P
authors.lastname: Rehulka
authors.forename: Vladimír
authors.initials: V
authors.lastname: Kovácik
authors.forename: Vladimír
authors.initials: V
authors.lastname: Pätoprstý
authors.forename: Pavol
authors.initials: P
authors.lastname: Kovác
mesh_terms: D000838:Anions / Q000737:chemistry; D002240:Carbohydrate Sequence; D007202:Indicators and Reagents; D008969:Molecular Sequence Data; D011134:Polysaccharides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D053719:Tandem Mass Spectrometry; D041241:Vibrio cholerae O1 / Q000737:chemistry*
chemical_list: D000838:Anions; D007202:Indicators and Reagents; D011134:Polysaccharides