铵锌镉还原法测试硝酸盐氮、氧同位素方法研究

Determination of the nitrogen and oxygen isotopic composition of dissolved nitrate by ammonium-zinc-cadmium reduction method

本研究利用铵锌镉还原法将海水、湖水和自来水水体中硝酸盐转化为N_(2)O气体测试氮、氧同位素,结果表明当反应体系的pH值在6~8之间,NO^(-)_(3)还原为NO^(-)_(2)的转化率大于95%,NO^(-)_(2)还原为N_(2)O的转化率大于99%。配置5种丰度的硝酸盐氮、氧同位素标样,将实验结果与理论值绘制校准曲线,氮同位素校准曲线斜率为0.48,相关性良好(R^(2)=0.9998),5种丰度δ^(15)N_(N_(2)O)标准偏差在0.18‰~0.43‰之间(n=5);氧同位素校准曲线斜率为0.70,相关性良好(R^(2)=0.9996),5种丰度δ^(18)O_(N_(2)O)标准偏差在0.27‰~0.46‰之间(n=5)。铵锌镉还原法与镉柱还原法测定硝酸盐氮、氧同位素结果的精密度和准确度一致,同时海水、湖水和自来水3种不同类型水样的硝酸盐氮、氧同位素测试数据满足实验要求,而且在实验流程的简洁性和高效性方面更具优势。

The ammonium-zinc-cadmium reduction method was used to convert nitrate to nitrous oxide for nitrogen and oxygen isotopic abundance analysis.In water reaction system with pH between 6 and 8,the efficiencies of nitrate reduction to nitrite were above 95%,and the efficiencies of nitrite to nitrous oxide using sodium azide in acetic acid buffer were higher than 99%.An excellent correlation between the knownδ^(15)N andδ^(18)O values of nitrate and the measuredδ^(15)N andδ^(18)O values of nitrous oxide exhibited a slope of 0.48 for nitrogen and 0.70 for oxygen,respectively,with both R^(2) values of 0.9998.The standard deviations ofδ^(15)N of 5 nitrogen compositions of N_(2)O were between 0.18‰and 0.43‰(n=5).The standard deviations ofδ^(18)O were between 0.27‰and 0.46‰(n=5).The results show that the precision and accuracy of the test for determination nitrogen and oxygen isotopes of nitrate are the same with other chemical conversion methods.Meanwhile,the data of nitrate nitrogen and oxygen isotopes of different types of water samples meet the experimental requirements.Furthermore the experimental process is also simpler and more efficient with advantage of lower cost.