An evaluation of acid disazo dyes by chloride determination and paper chromatography

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Abstract
Different commercial samples of 13 acid disazo dyes have been subjected to ascending paper chromatography and examined for moisture and NaCl content, the latter being determined by potentiometric titration. Moisture in most cases accounts for less than 10% of the weight, but the content of NaCl is frequently high; only one half of the samples tested containing less than 30%, and one third containing more than 55%. Ascending paper chromatography in the solvent system n-butanol-pyridine-water (1:5:4 by volume), which separates the samples into discrete spots, has revealed the presence of coloured impurities in many dyes. Detailed results are reported.