1982 Volume 31 Issue 9 Pages 538-540
Sodium 2-bromo-4, 5-dihydroxyazobenzene-4'-sulfonate (BDAS) reacts with traces of lead in a weakly basic medium in the presence of cetyltrimethylammonium chloride (CTMAC) to form a water soluble ternary complex. The combining ratio of lead and BDAS in the ternary complex was shown to be 1 : 2. The ternary complex having its absorption maximum at 530 nm is quantitatively formed between pH 8.4 and 9.1, and is stable for at least 3 h. The absorbance of the complex was constant provided that the BDAS, CTMAC, and boric acid concentrations were more than 1.2 × 10 -4M, 2.0 × 10-4M, and 0.03 M, respectively. Absorbance of the reagent blank was effectively reduced by addition of excessive borate ions. The procedure is as follows: Transfer the sample solution containing up to 80 μg of lead to a 25 ml volumetric flask. Add 2 ml of 2.5× 10-3 M BDAS, 10 ml of 0.1 M boric acid (adjusted to pH 8.7 with sodium hydroxide), 3 ml of 0.01 M CTMAC, and 2.5 ml of 1 M potassium nitrate. Dilute to the mark with water and measure the absorbance at 530 nm using the reagent blank as a reference. Beer's law was obeyed over the range 0 80μg of lead. The apparent molar absorptivity of the ternary complex is 4.49 × 104 cm-1 mol-1 1 at 530 nm and the sensitivity of the reaction was 4.6 × 10-3 μg cm-2. Interfering cations such as cobalt, cadmium, copper, and zinc were masked by addition of potassium cyanide.
