塩化セチルトリメチルアンモニウムの存在下2-プロモ-4,5-ジヒドロキシアゾベンゼン-4'-スルホン酸ナトリウムによる鉛の吸光光度定量

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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^<-4> M, 2.0 × 10^<-4> M, 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 *g 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 GTMAC, 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 0〜80 *g of lead. The apparent molar absorptivity of the ternary complex is 4.49 × 10_4 cm^<-1>1 mol^<-1> 1 at 530 nm and the sensitivity of the reaction was 4.6 × 10^<-3> *g cm^<-2>. Interfering cations such as cobalt, cadmium, copper, and zinc were masked by addition of potassium cyanide.
1982-09-05