An Evaluation of the Metachromasia of Bromophenol Blue

The heterogeneity of bromophenol blue from different commercial sources was revealed by paper chromatography. Isopropanol:ammonia:water (20:1:2) as the solvent system gave the best separation. A variety of impurities: violet, pink, light blue and yellow coloured ones were observed. Two of the yellow fractions showed a spectral shift to red in the presence of ammonia vapour. The respone of the main dye component with the anionic chromotropes such as heparin and hyaluronate was found to be metachromatic similar to that exhibited by the dye solution and not due to a polychromatic effect. The metachromatic effect was blocked by FeCl₃ as in the case of cationic dye metachromasy. The observed metachromatic colour is not one of the colours which characterize those resulting from changes caused by pH.