High pressure liquid chromatographic determination of thioglycolic acid in cold wave fluids and depilating creams

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Abstract
A high pressure liquid chromatographic (HPLC) method is described for the determination of thioglycolic acid in hair waving fluids and depilatories. Prior to chromatography, the acid is converted into a yellow-colored nitrobenzoxadiazole (NBD) derivative to permit HPLC detection at 464 nm. Optimum derivatization conditions could be obtained when 0.01% aqueous solutions of thioglycolic acid were heated with NBD-Cl at pH 7. Hair waving fluids and depilatories are simply diluted with an aqueous buffer of pH 7 and clarified and filtered, before the derivatization procedure. An internal standard Sunset Yellow FCF, Color Index nr. 15985, is added to the mixture before performing ion-pair reverse phase HPLC. A reverse phase C18 column is used. The mobile phase is aqueous methanol, to which the counter ion, tetrabutyl-ammonium phosphate, is added. Recoveries ranged from 97.8-100.7%. The proposed method permits a resolution of other possible mercaptocompounds such as thiolactic acid and thioglycerol. Sixty market samples of cold wave fluids and depilatories were analyzed by the method and the results compared with data obtained by iodometric titration.