Dual-modification strategy of Co and g-C.sub.3N.sub.4 to CuS for efficient colorimetric determination of thioglycolic acid in daily cosmetics

A conventional colorimetric method based on CuS-catalyzed H.sub.2O.sub.2 is improved by a dual-modification strategy and employed for thioglycolic acid (TGA) determination. The doping of Co(II) can enhance ion exchange efficiency. Meanwhile, the modification of g-C.sub.3N.sub.4 can increase specific surface area and decrease unspecific aggregation. The constructed g-C.sub.3N.sub.4/Co-CuS nanocomposite exhibited a favorable catalytic feature. A Michaelis constant (K.sub.m) value of 0.02 mM has been achieved, which is 1/160 of those of CuS and horseradish peroxidase (HRP). The g-C.sub.3N.sub.4/Co-CuS displays a rapid color response in 3 min and resulted in a stable measurable signal within 10 min. In the determination procedure, the sulfhydryl contained in TGA is capable of preventing TMB oxidation via competing the ·OH produced by catalysis and caused a color distinction that is related to the TGA amount. The distinctions of absorbance ([lambda].sub.max = 652 nm) of different concentrations of TGA are recorded. Linearity is obtained in the ranges of 2.5 - 20 [micro]M and 20 - 160 [micro]M, and the LOD is 0.14 [micro]M. In the real sample assays of perm agent and Qianhu lake water, the recoveries were 96.70 - 106.84% and 100.21 - 101.90%, respectively. This demonstrates that the proposed dual-modification strategy for CuS contributes to highly efficient and convenient determination of TGA in daily cosmetics and water analysis.