Identification of Coal Tar Dyes by Reversed-Phase TLC/FABMS with a Sample Condensation Technique

Abstract

We have established a reversed-phase thin-layer chromatography/fast-atom bombardment mass spectrometric (TLC/FABMS) method incorporating an analyte condensation technique for the identification of the 12 permitted coal tar dyes in Japan. Use of “magic bullet” as a matrix enabled us to measure the FAB mass spectra of the food coal tar dyes except for Food Blue No. 2 (indigo carmine). Two solvent systems, methyl ethyl ketone-methanol-5% aqueous sodium sulfate solution=1:1:1 and methanol-acetonitrile-5% aqueous sodium sulfate solution=3:3:10 were selected for the separation of the xanthene dyes and the others, respectively on a reversed-phase TLC plate. The condensation technique, which concentrates a diffused sample spot on a TLC plate, improved the detection limit 150-fold with good reproducibility. The established TLC/FABMS method was successfully applied to identification of coal tar dyes in commercial foods.