Abstract
Pretreatment of trace amount of sulfate ion in aqueous solution with the barium chromate-acidic suspension method (JIS) and quantitative determination of sulfate ion by atomic absorption spectrometry were studied. The whole procedure is consisted of (i) quantitative precipitation of the sulfate ion with barium chromate-acidic suspension, (ii) filtration of the precipitate, and (iii) analysis of the liberated chromate ion by atomic absorption spectrometry. Using the synthesized solution containing Cr (VI), effects of the amount of various substances, such as NH4OH, NH4OH containing Ca, mixed acid, mixed solution, ethanol and some sodium compounds, on the atomic absorbance of Cr (VI) were examined. The best results were obtained under the following conditions. To a 10 ml of the sample solution, add 4 ml of the barium chromate-acidic suspension, 1 ml of the ammonium hydroxide solution containing Ca and 10 ml of ethanol. Shake for 1 min, and filter through a dried filter paper, and then, measure the atomic absorbance of the filtrate. Under the optimum condition, the recovery of sulfate ion was 92 % or better. The proposed method was compared with the spectrophotometric method (JIS) for the determination of the sulfate ion at ppm level in the sample such as the elution of colored organic and inorganic pigments. Agreement between the two methods was within the acceptable allowance when the sample solution was colorless. In general, it is difficult to use the spectrophotometric method, prescribed in JIS K 0102-1974, for the analysis of most of the colored sample solutions. But the proposed method was applicable to the colored sample solutions as well as to the colorless.
