Formation of the bisulfite anion (HSO(3)             (-) , m/z 81) upon collision-induced dissociation of anions derived from organic sulfonic acids.
In the negative-ion collision-induced dissociation mass spectra of most organic sulfonates, the base peak is observed at m/z 80 for the sulfur trioxide radical anion (SO(3) (-·) ). In contrast, the product-ion spectra of a few sulfonates, such as cysteic acid, aminomethanesulfonate, and 2-phenylethanesulfonate, show the base peak at m/z 81 for the bisulfite anion (HSO(3) (-) ). An investigation with an extensive variety of sulfonates revealed that the presence of a hydrogen atom at the β-position relative to the sulfur atom is a prerequisite for the formation of the bisulfite anion. The formation of HSO(3) (-) is highly favored when the atom at the β-position is nitrogen, or the leaving neutral species is a highly conjugated molecule such as styrene or acrylic acid. Deuterium-exchange experiments with aminomethanesulfonate demonstrated that the hydrogen for HSO(3) (-) formation is transferred from the β-position. The presence of a peak at m/z 80 in the spectrum of 2-sulfoacetic acid, in contrast to a peak at m/z 81 in that of 3-sulfopropanoic acid, corroborated the proposed hydrogen transfer mechanism. For diacidic compounds, such as 4-sulfobutanoic acid and cysteic acid, the m/z 81 ion can be formed by an alternative mechanism, in which the negative charge of the carboxylate moiety attacks the α-carbon relative to the sulfur atom. Experiments conducted with deuterium-exchanged and deuterium-labeled analogs of sulfocarboxylic acids demonstrated that the formation of the bisulfite anion resulted either from a hydrogen transfer from the β-carbon, or from a direct attack by the carboxylate moiety on the α-carbon.
Center for Mass Spectrometry, Department of Chemistry, Chemical Biology, and Biomedical Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA.
Freneil B
FB
Jariwala
Ryan E
RE
Wood
Upul
U
Nishshanka
Athula B
AB
Attygalle
D000838:Anions / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry; D055598:Chemical Phenomena; D003544:Cysteic Acid / Q000737:chemistry; D005740:Gases / Q000737:chemistry; D013058:Mass Spectrometry; D008958:Models, Molecular; D013447:Sulfites / Q000737:chemistry*; D013451:Sulfonic Acids / Q000737:chemistry*
D000838:Anions; D002264:Carboxylic Acids; D005740:Gases; D013447:Sulfites; D013451:Sulfonic Acids; D003544:Cysteic Acid; C042345:hydrogen sulfite