F. Beck

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

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.

The Identification of Some Acid Disazo Dyes by Paper Electrophoresis of their Reduction Products

Trypan blue, Niagara blue 2B, Niagara blue 4B, Afridol blue, Evans blue, Niagara sky blue 6B, Niagara blue 5B and Chlorazol blue G cannot be distinguished by their colour or their behaviour on paper chromatography. They may, however, be identified by paper electrophoresis at pH 4 of the products obtained by reduction of the azo linkages with sodium dithionite (Na2S2O4).