Improved Spectrophotometric Determination of Bismuth (III) with Bromopyrogallol Red in Mixed Surfactants-Application to Waters and Veterinary Preparation

A simple and sensitive spectrophotometric method for the determination of trace amounts of bismuth is established. The method is based on the reaction of bismuth with bromopyrogallol red at pH 3 in the presence of a mixture of cetylpyridinium chloride and triton X-100 surfactants to form a blue coloured complex which shows maximum absorbance at 644 nm. A plot of absorbance with bismuth concentration gives a straight line indicating that Beers law has been obeyed over the range 3-150 μg/25 ml, i.e., 0.12-6 ppm with a molar absorptivity of 3.3×10 l.mol.cm and Sandells sensitivity index of 0.006 μg.cm. The interfering effect of a number of common captions and anions in the presence of comosite mixture (NaF and tartaric acid) and ascorbic acid as masking agents has been studied. The effect of common excipients has also been examined. The method has been applied successfully to the determination of bismuth in water samples and a veterinary preparation.