The determination of thiol-containing compounds in biological materials is important for studies on the active sites of enzymes, in pharmacodynamic studies of drugs having a thiol group or in diagnosis of some kinds of diseases[1]. The selective reaction of chemical reagents with reduced protein thiols is utilized to prevent cross-linking of cysteine-containing peptides in common proteomics workflows and is applied widely in discovery and targeted redox investigations of the mechanisms underlying physiological and pathological processes[2].