Spectrophotometric determination of copper (II) with sodium 2-bromo-4, 5-dihydroxyazobenzene-4′-sulfonate in the presence of cetyltrimethylammonium chloride

Abstract

Sodium 2-bromo-4, 5-dihydroxyazobenzene-4′-solfonate (abbreviated as BDAS) reacts with traces of copper(II) in a neutral medium in the presence of cetyltrimethylammonium chloride (CTMAC) to form a strongly colored ternary complex. The complex has an absorption maximum at 530 nm, and the maximum absorbance was obtained in the pH range from 6.4 to 8.3. The absorbance of the complex was constant provided that the BDAS and CTMAC concentrations were more than 1.0×10-4 M and 4.0×10-4 M respectively. Absorbance of the reagent blank was effectively reduced by addition of excessive sodium borate. The procedure is as follows: Transfer the sample solution containing up to 26 μg of copper(II) to a 25 ml volumetric flask. Add 4 ml of 1×10-3 M BDAS, 10 ml of 0.2 M phosphate buffer (pH 7.0) containing 0.04 M sodium borate, 3 ml of 0.01 M CTMAC and 2.5 ml of 1 M potassium chloride. 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 026μg of copper(II). The apparent molar absorptivity of the ternary complex is 4.8×104 cm-1 mol-1 l at 530 nm, and Sandell's sensitivity is 1.4×10-3 μg cm-2. The combining ratio of copper(II) and BDAS in the ternary complex was shown to be 1:2. Iron(III), aluminum, galium, indium, titanium(IV) and molybdenum(VI) interfered with the determination of copper (II) even when present at microgram levels. © 1976, The Japan Society for Analytical Chemistry. All rights reserved.