THE THIN-LAYER CHROMATOGRAPHY OF VAT DYES

The identification and separation of vat dyes by thin layer chromatography has been investigated with reducing and non-reducing systems. The results showed that the chromatograms on silica gel plates obtained by non-reducing systems at 100 or 120-degrees-C were fast, reproducible and easy to control. Nine non-reducing eluents were developed, producing good migration and resolution of 21 vat dyes. Analyses of the chromatograms revealed that the R(f) values varied with the temperature of the system, the chemical structure of the vat dyes and the nature of adsorbent, as well as with the eluents used. The effects of molecular masses of the vat dyes on the R(f) values were less significant. Despite the successful use of a novel reducing agent for vat dyes, the chromatography of reduced dye was largely unsatisfactory. The use of reversed-phase t.l.c. plates was examined and showed little benefit.