Separation and identification of food dyes by thin-layer chromatography/liquid secondary ion mass spectrometry

In order to separate and identify rapidly the 11 food dyes that are permitted in Japan, a thin-layer chromatographic/liquid secondary ion (LSI) mass spectrometric method was established. The characteristic features of these food dyes under fast atom bombardment and LSI mass spectrometric conditions were carefully investigated using various matrices. While glycerol enhanced reduction of them, magic bullet depressed the reduction to give the molecular ion species with the theoretical isotopic abundances. The two solvent systems, methanol-methyl ethyl ketone-10% sodium sulphate (1:1:3.5) (solvent A) and methanol-acetonitrile-10% sodium sulphate (3:3:10) (solvent B) were selected for separation of the xanthene dyes and the others, respectively by use of a reversed-phase thin-layer chromatographic plate prepared by ourselves. A method was also devised to concentrate a diffused spot on the plate using thioglycerol. The established thin-layer chromatographic/LSI mass spectrometric method was finally applied to identification of an unknown food dye from a candy.