The Method of Separation and ldentification of Azo Dyes having NO2 Groups.

For the separation and identification of azo dyes having NO2 groups, thin-layer chromatography, alkali reaction and sodium borohydride reaction were successfully used. A clear separation of six kinds of dyes were achieved by thin-layer chromatography with aluminium oxide as adsorbent and toluene-petroleum ether (7 : 3) saturated with water as developing solvent. The position of maximum absorption of these dyes in alcoholic sodium hydroxide solution shifted to a longer or a shorter wavelength compared with toluene solution. The absorbance of Flaming Red was most stable, whereas that of Permanent Orange decreased after a few minutes. These dyes exhibited complicated changes in the absorption maximum and absorbance with sodium borohydride.