Identification of Coal Tar Dyes in Cosmetics and Foods Using Reversed Phase TLC/Scanning Densitometry.

Abstract

A simple and rapid analysis of coal tar dyes in cosmetics and foods was established using reversed phase TLC/scanning densitometry. Forty-five kinds of coal tar dyes were able to be separated completely on reversed phase TLC plates by the complementary use of 4 solvent systems. Solvent system A : acetonitrile-methanol-5% aqueous sodium sulphate solution (3 : 3 : 10, v/v), solvent system B : methyl ethyl ketone-methanol-5% aqueous sodium sulphate solution (1 : 1 : 1, v/v), solvent system C : acetonitrile-methanol-5% aqueous sodium sulphate solution (1 : 1 : 1, v/v), solvent system D : acetonitrile-dichloromethane-5% aqueous sodium sulphate solution (10 : 1 : 5, v/v). Then we measured visible absorption spectra of coal tar dyes on the developed reversed phase TLC plates by scanning densitometry to identify these coal tar dyes. The proposed method was successfully applied to the identification of coal tar dyes in commercial products.