Characterization of solution-phase and gas-phase reactions in on-line electrochemistry—thermospray tandem mass spectrometry

Abstract

Electrochemistry was used on-line with high-performance liquid chromatography—thermospray tandem mass spectrometry to provide insigh into the solution-phase decomposition reactions of electrochemical generated oxidation products. Products formed during electrooxidation were monitored as the electrode otential was varied. The solution reactions which follow the initial electron transfer at the electrode are affected by teh vaporizer tip temperature of the thermospray probe and the composition of the thermospray buffer. Eitehr hysdrolysis or ammnolysis reactions of the initial electrochemical oxidation products can occur with pH 7 ammonium acetate buffer. Both the electrochemically generated and the synthesized disulfide of 6-thiopurine decompose under thermospray conditions to produce 6-thiopurine and purine-6sulfinate. Solution-phase studies indicate that nucleophilic and electrophilic substitution reaction with purine-6-sulfinate result in the formation of purine, adenine, and hypoxanthine. Products were identified and characterized by tandem mass spectrometry. This work shows the first example of high-performance liquid chromatography used on-line with electrochemsitry to separate stable oxidation products prior to analysis by thermospray tandem mass spectrometry. In additon. solution-phase and gas-phase studies with methylamine show that the site of teh nucleophilic and electrophilic reactions is probably inside the thermospray probe. Most importantly, these results also show that the on-line combination of electrochemistry with thermospray tandem mass spectrometry provides valuable information about redox and associated chemical reactions of biological molecules such as the structures of intermediates or products as well as providing insight into reaction pathways.