次亜硝酸の定量法

抄録

A colorimetric determination of hyponitrous acid based on the method of oxime estimation, previously described by Akita, was discussed and some improvements on the procedures have been made.
At first, a sample crystal of sodium hyponitrite is solved in an acetate buffer at pH 3_??_4, since the aqueous solution of hyponitrous acid at alkalinity is unstable. Immediately after diluting it with water to an appropriate concentration (0.1_??_1.5μg nitrogen per 10ml), 10ml of the solution thus obtained (pH about 6) is mixed with 1 ml of 1% sodium sulfanilate, 0.3ml of 0.1 N iodine (in 2% KI) and 0.15ml of 0.5 N NaOH. After 30min. at room temperature, into the mixture are added 1ml of 30% acetic acid, 0.15ml of 0.5 N HC1, 0.3ml of 0.1 N sodium thiosulfate and 1ml of sat. α-naphthylamine.
After 30 min. at room temperature, red color developed is measured with spectrophotometer at 525 mμ. In this instance, however, after the step of addition of acetic acid, an interval of the adding of each reagent must be kept as short and constant as possible, appr. one min., since the intermediate compound produced in this step is easily decomposed. In addition, in order to correct the data if necessary, a constant concentration of nitrous acid must be determined in the same manner as a control.
Extinction was proportional to the concentration of hyponitrous acid of about 10^-6 M. This method involves the reaction which is shown according to the following equation, since hyponitrous acid was oxidized quantitatively to nitrous acid.
H₂N₂O₂ + O₂=2HNO₂