Abstract
Radio-tracer and photometrical studies were made for the determination of the micro amount of cadmium(II) with 1-(2-pyridilazo)-2-naphthol (PAN) in a digested solution obtained by oxidizing biological materials with potassium permanganate and a mixture of H2SO4 and HNO3.
A scheme of photometric analysis of cadmium(II) was designed and the behaviour of cadmium(II) and interfering ions in every step of the scheme was examined radiochemically by using Ge(Li) detector and a 4000-channel pulse height analyser, and the following results were obtained. (1) Cadmium(II) was coprecipitated quantitatively with antimony(III) sulfide from solutions of pH 2.5 (optimum)4.0. The quantitative coprecipitation of cadmium(II) was also observed at pH 2.5 when copper(II) was used as the carrier instead of antimony(III). (2) The extraction with 4, 4, 4-trifluoro-1-(2-thienyl)-1, 3-butanediene (TTA) chloroform solution showed that copper(II) was extracted quantitatively in the pH range of 3 to 10, mercury(II) was extracted partialy in the same pH range, and other ions such as cadmium (II), arsenic (III) and antimony (III) were not extracted at the pH range of 2 to 12. (3) The optimum pH for extraction of cadmium(II) with pyridine-chloroform solution from 0.1 M thiocyanate solution was 4 to 7. Below pH 10, copper(II) was extracted quantitatively. Mercury(II), arsenic(III) and antimony(III) were not extracted at pH range of 2 to 12. (4) The optimum pH for the extraction of cadmium(II) and copper(II) with PAN-chloroform solution was 10 to 11 and 4 to 11, respectively. Mercury(II) was extracted partialy, and neither arsenic(III) nor antimony(III) were extracted at the pH range of 2 to 12.
From these results, the following procedure was established. After 2 mg of antimony(III) or copper(II) was added to 100 ml of the sample solution, the sulfide was precipitated with H2S at pH 2.5. The sulfide precipitate was collected and dissolved in aqua regia, and the solution was evaporated to dryness. The residue was dissolved in dil. HCl, and copper(II) was eliminated at pH 3.0 by extracting with TTA-chloroform solution. The aqueous phase was made to 0.1 M thiocyanate solution and adjusted to pH 5.0, then cadmium(II) was separated from mercury(II) by extracting with pyridine-chloroform solution. The chloroform solution was evaporated to dryness, and the organic matters were decomposed with HNO3. The residue was dissolved in dil. H2SO4, and potassium sodium tartrate was added to the solution for masking tin(II) and lead(II). The pH of the solution was adjusted to 10.5, and PAN-methanol solution was added. After the solution was let stand for more than 5 minutes, the cadmium-PAN complex was extracted with chloroform, and the absorbance of the chloroform solution was measured at 555 nm.
The overall recovery of the procedure was examined by adding 115Cd tracer to the acid-digested solution of biological materials containing about 10 μg of cadmium(II), and the recovery was 91±2%.
