HPLC determination of thioglycolic acid and other aliphatic thiols in cosmetic formulations using ethacrynic acid as precolumn derivatization reagent

Limits imposed on the usage of thioglycolic acid, its salts and esters in cosmetic formulations require selective and sensitive analytical methods for their determination. In this study a convenient and reliable method based on high-performance liquid chromatography (HPLC) has been developed. The method involves a precolumn reaction of the thiol compounds with ethacrynic acid to give thiol adducts which can be separated by reversed-phase liquid chromatography and detected at λ= 273 nm.
The derivatization reaction proved to be quantitative under mild conditions (20 min at pH 7.4 and room temperature) and the chromatographic conditions allowed thioglycolic acid, glyceryl monothioglycolate, thiolactic acid, and thioglycolic acid ethyl ester to be discriminated.
The proposed method was successfully applied to the analysis of commercial cosmetic formulations containing thioglycolic acid and glyceryl monothioglycolate, fulfilling the requirements of a general and selective method for the analysis of aliphatic thiols in cosmetics.