1978 Volume 27 Issue 7 Pages 405-409
1-Pyrrolidinecarbodithioate ion (hereinafter abbreviated to pdtc) forms a sparingly soluble precipitate with copper (II) ion. This precipitate was dissolved in water in the presence of nonionic surfactant such as Triton X-100 (alkylphenolpolyoxyethylene ether) and gave an absorption maximum at 440 nm. This color development was applied to the spectrophotometric microdetermination of copper (II). The recommended procedure for the determination of copper (II) with pdtc is as follows: Take into a 25 cm3 measuring cylinder with ground stopper an aliquot of sample solution containing less than 95.3 μg of copper (II). Add 4 cm3 of 1.25× 10-1 mol dm-3 EDTA solution, and 1 cm3 of 1 mol dm-3 acetate buffer (final pH of the solution adjust to 4.76.1). Adjust the solution to 16 cm3 with water. Add 2 cm3 of 10.0 (v/v) % Triton X-100 solution and 2 cm3 of 1.0 × 10-1 mol dm-3 pdtc solution. Measure the absorbance at 440 nm against water. A linear relationship was obtained within the range of (1.395.3) μg Cu (II) /20 cm3. The molar absorption coefficient at 440 nm was 1.57 × 104. The ions which interfere seriously in this method are Cd (II), Fe (III), Mn (II), Co (II) and CN-. However, at the concentration of 2.5×10-2 mol dm-3 of EDTA, zinc (II) up to 70 mg, iron (III) up to 0.8 mg, cadmium (II) up to 0.1 mg, manganese (II) up to 0.3 mg and cobalt (II) up to 0.03 mg had no interference on the determination of 63.5 μg of copper (II) in 20 cm3. This method does not need solvent extraction and is rapid, and simple. The composition ratio of copper (II) to pdtc in the dissolved yellow colored complex was 1:2 by Yoe-Jones plot and the continuous variation plot. This agreed with the results from gravimetric and solvent extraction analyses. Therefore it is assumed that the precipitate of Cu (pdtc)2 is highly soluble in micelles of Triton X-100 formed in water.
