クロムアズロールSとゼフィラミンによる鉄の存在における微量のアルミニウムの吸光光度定量

A highly sensitive method for the spectrophotometric determination of aluminum with Chromazurol S (CAS) and zephiramine have been developed as described in the previous paper {Bunseki Kagaku, 21, 997 (1972)}. Though interference with iron was masked by an addition of thioglycolic acid in that case, a negative effect by the absorbance of aluminum complex was caused. The writer found that the negative influence by thioglycolic acid could be removed by additions of some electrolytes, especially ammonium salts and its derivatives such as hexamine, ammonium chloride and trimethylbenzylammonium chloride. But ammonium acetate and urea which were a sort of acetate and of non-electrolyte respectively was ineffective. Optimum volumes of these reagents were above 2 ml for 1 M hexamine solution, above 3 ml for 1 M ammonium chloride solution and above 3 ml for 1 M trimethyl benzylammonium chloride solution. The absorbance had the highest and fixed value in the range of pH 4.755.2. However the color of the complex was faded catalytically by thioglycolic acid in the presence of iron at pH above 5.1, the pH was adjusted to 4.9. In the case of the alkaline solution of hexamine the absorbance was faded slightly with standing, so the pH of the hexamine solution had to be adjust to 5 with hydrochloric acid. Interference with up to 10 mg of iron was masked by adding 0.81.5 ml of 8% thioglycolic acid.<BR>This method was applied to the determination of aluminum in malleable cast iron. The recommended procedure was as follows.<BR>Take 0.2 g of sample into a 100 ml quartz beaker and dissolve in 1 ml of concentrated hydrochloric acid and 510ml of water with heating. Add 0.5 ml of concentrated nitric acid and boil up in order to remove nitrogen oxide. Filter the solution, wash the residue on the filter paper with hydrochloric acid (1+100), and dilute the filtrate to 100 ml with water. To an aliquot of the solution containing up to 5 μg of aluminum, add 1 ml of 8% thioglycolic acid, 1 ml of 0.2% CAS solution, 5 ml of 0.5% zephiramine solution, and 4 ml of 7% hexamine solution. Adjust the pH to 4.9 with 0.5 Msodium hydroxide solution and dilute to 25 ml with water. After the solution has stood for 30 minutes, measure the absorbance at 620 nm against the reagent blank which prepared from aluminumless iron by the same procedure as used for the sample.<BR>The calibration curve was quite linear for 0.15μg of aluminum in 25 ml. The molar absorptivity was 1.15×10⁵, The relative standard deviation was 15% for the determination of 0.0020.06% of acid soluble aluminum in malleable cast iron.<BR>In the case of determination of aluminum by Eriochrome Cyanine R(ECR) and zephiramine method interference with thioglycolic acid and the acetate could be also masked by an addition of ammonium chloride at pH 5.9.