Methods for quantification of oxidised and reduced forms of glutathione (GSSG and GSH) and cysteine (CSSC and CSH) and the disulphide glutathione-cysteine (GSSC) resulting from the oxidation of the mixture of CSH and GSH are performed by RP-HPLC with coulometric and UV detection after separation of these compounds by size-exclusion fast protein liquid chromatography. The fractionation of the disulphides (GSSG, GSSC and CSSC) was achieved by size exclusion using a Superdex peptide column coupled with an UV detection at 254 nm. The conditions of separation of these compounds by RP-HPLC were optimised using the response surface methodology. Optimal peak resolution and retention times were obtained on a C18 YMC ODS AQ column with 20 mM of ammonium phosphate at pH 2.5 and 2% of acetonitrile in the elution phase. In these experimental conditions, CSH, CSSC, GSH and GSSG were eluted within 20 min. Coulometric detection enabled a sensitivity 100 times higher for the disulphides than the UV detection at 220 nm. These methods were applied to follow the consumption of thiols and the disulphide formation by three oxidising systems, sulphydryl oxidase, glutathione dehydroascorbate oxidoreductase and potassium bromate. This study revealed that the relative proportions of the disulphides formed were similar for the three oxidising systems when the reactions are in their state of equilibrium.