A robust ICPMS-based method is introduced to obtain relative and absolute quantification of sulfenic acid (SA) in peptides and proteins. A new metal-containing reagent (Ln-DOTA-Dimedone) devised to react specifically with SA has been developed. The lanthanide-containing metal-coded affinity tag (Ln-MeCAT) was used to quantify thiol residues. We presented two approaches which allow the parallel and consecutive determination of SA and thiols in peptide and protein samples. The high sensitivity, structure-independent signal, and multiplexing capabilities of ICPMS together with the specificity of Ln-DOTA-Dimedone and Ln-MeCAT toward sulfenic acid and thiol residues, respectively, allow the characterization of various biological states and offer closer insight onto thiol-sulphenic acid equilibria which are involved in intracellular redox-mediated events altering structure and function of proteins in important diseases.