インドフェノール青吸光光度法によるアンモニア分析における二酸化硫黄の妨害除去

概要

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According to the present JIS method, which describes the determination of ammonia(NH_3) in flue gas, the presence of more than 10 times as much sulfur dioxide(SO_2) as NH_3 results in interference with the determination of NH_3 by indophenol blue absorptiometry. The magnitude of interference from the coexisting sulfur dioxide and its elimination of described. The magnitude of interference was investigated using NH_3 and SO_2 standard gases. Both standard gases were bubbled through a 0.5% boric acid solution independently and simultaneously; 0〜200 times as much SO_2 as NH_3 by mole was bubbled through a boric acid solution. The absorbed NH_3 and SO_2 were determined by coulometry and alkalimetry, respectively. The magnitude of interference was dependent upon the amount of SO_2 absorbed in the boric acid solution, not the molar ratio of SO_2 to NH_3. More than 100 μmol SO_2 led to a serious decrease in the absorbance. In the case of a 20 liter sample, it was found that more than approximately 110 volppm of SO_2 gave a lower analytical value of NH_3. The interference could be eliminated by bubbling 400 ml of oxygen at a flow rate of about 70 ml min^<-1> through a boric acid solution containing the absorbed gas sample.
2001-09-05