INVESTIGATION OF SOME THIOSULFONATE DERIVATIVES BY MEANS OF CHEMICAL-IONIZATION AND TANDEM MASS-SPECTROMETRY

A number of thiosulfonate derivatives have been investigated by means of ammonia chemical ionization (NH3-CI), electron impact ionization (E I) and mass-selected collision induced dissociation (CID). For most of the compounds investigated, the NH3-CI positive-ion mass spectra exhi bit the addition ion, [M + NH4]+, as the dominant species, which impli es that the proton affinities of the compounds investigated are less t han the proton affinity of NH3. Deviation from true chemical ionizatio n conditions resulted in efficient dissociation of the addition ion to yield substantial amounts of the protonated molecule, [M + H]+. The m ajor fragment ions observed in the EI mass spectra and in the CID spec tra indicate the cleavage of the sulfur-sulfur bond to be more efficie nt than other competing cleavages. This and other experimental observa tions are discussed.