Commercial Orange I was submitted to paper chromatography with developing solvent of BuOH: EtOH: 1% NH4OH (6:2:3, by volume) and the subsidiary dye fraction was extracted from paper with dil. NH4OH. After evaporation of solvent, the residue was dissolved in water. This solution was analysed by high-voltage paper electrophoresis described in the previous report [This Journal, 2, No. 2, 44 (1961)].
As a result, 2-p-sulfophenylazo-1-naphthol was identified besides Orange II in commercial samples of Orange I.
Spectrophotometric determination of these two subsidiary dyes was successively carried out.
There is a marked difference in the absorption cruve of these dyes which are dissolved in 0.1N NaOH respectively. It is possible, therefore, to determine the amount of each dye present in a mixture of the two simultaneously.
It was recognized that 2-p-sulfophenylazo-1-naphthol was present about 3-5% in almost commercial samples of Orange I.