Photometric determination of thioglycolic acid in cosmetics by using a stopped-flow reverse flow-injection system and the formation of gold nanoparticles

The positive effect of thiol compounds as reducing agents in the synthesis of gold nanoparticles in the presence of a micellar medium of Triton X-100 has been photometrically studied using a reverse flow-injection system which operates in the stopped-flow mode (SF-rFIA). The analytical usefulness of this new system has been assessed by its application to the determination of thioglycolic acid (TGA), which was chosen as the analyte model. The dynamic range of the calibration graph was 5.97–80 μmol L−1, and the detection limit was 1.73 μmol L−1. The behaviour of other thiol compounds on the system has been also studied. The precision of the method, expressed as relative standard deviation, ranged between 1.5 and 2.3%. The method was applied to the determination of TGA in several cosmetic samples with acceptable recoveries in all instances, which ranged between 90.32 and 101.46%.