チモールを用いるアンモニア窒素の光度定量法

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The sensitive photometric method, using thymol, reported by Roskam and de Langen {Anal. Chim. Acta, 30, 56 (1964)}, has been examined, and the following factors were found to be important in this method : (1) The pH of the solution at the step of adding hypochlorite (pH 9.810.3), (2) the time interval between the addition of hypochlorite and that of thymol (within 30 seconds), and (3) the pH of the colored solution (pH 11.511.9). The maximum color intensity was attained after 60 minutes and remained constant for at least 5 hours, when the solution was stored in dark place. No effect of temperature was observed in the range of 530°C. The absorbance per 1 μg nitrogen was 0.0165 (molar absorptivity=1.16×104) at 660 mμ by the following established procedure: Sodium hydroxide solution (1 M) is added to a weakly acidic sample solution (less than 30 ml) containing 36 μg of ammonia nitrogen, to which has been added one drop of phenolphthalein solution (0.1%), until pink color appears, and then 2 ml of sodium bicarbonate (0.06M)-sodium carbonate (0.075M) buffer solutions added to adjust the pH to 10. Then, 0.2 ml of sodium hypochlorite solution containing 0.3% active chlorine is added to the solution. After 20 seconds, 2.5 ml of a freshly prepared mixture of the equal volumes of thymol solution(10% in acetone) and sodium hydroxide solution (0.9M) is added to it. The resultant solution is transferred to a 50 ml measuring flask, and diluted to the mark with water. After standing for 1 hour in darkness, the absorbance of the colored solution is measured against the blank at 660 mμ.
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チモールを用いるアンモニア窒素の光度定量法

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