纳氏试剂法检测水中低浓度氨氮存在问题分析及方法改进探讨

针对采用《水质氨氮的测定纳氏试剂分光光度法》(HJ 535—2009)测定低浓度氨氮时存在的测不准问题,研究了药剂投加量、反应时间等因素对检测结果的影响,认为低浓度氨氮下的显色反应速度过慢是测定结果不准的原因,并据此提出利用强碱调节pH的方法加速反应进程。改良后的方法可以在0.2～1.2 mg/L氨氮浓度范围内呈现良好的线性关系,相关系数r为0.999 4。该方法具有较高的准确度和精密度,有效扩大了低浓度氨氮的检测范围,在实际样品检测中的回收率为102.5%～115.0%,可为准确测定水环境和饮用水中的氨氮浓度提供一种简便易行的手段。

Problems and Countermeasures of Nessler's Regent Spectrophotometry Method for the Determination of Low Concentration Ammonia Nitrogen in Water

To improve the precision and accuracy of Nessler''s regent spectrophotometry method, a national standard method of China, for the measurement of low concentration ammonia nitrogen in water, the impacts of regents as well as reaction time on the performance of measurements were investigated. The slow reaction rate with low ammonia nitrogen concentrations was regarded as the major reason of inaccurate measurement results, and a pH adjusting method by NaOH was adopted to accelerate the reaction. The results indicated that a perfect linear relationship was found between absorbance at 420 nm and ammonia nitrogen concentrations within the range of 0.2-1.2 mg/L, and the correlation coefficient was 0.999 4. The modified method showed a high precision and accuracy for the measurement of ammonia nitrogen and extended the range of measurement at low concentrations of ammonia nitrogen. The recoveries of ammonia nitrogen in actual samples were 102.5%-115.0%. Our finding may provide a feasible and accurate measurement method for the determination of ammonia nitrogen in water environment and drinking water.