摘要
目的:针对硝酸盐氮氧同位素新型预处理方法——细菌反硝化法尚存在的氧同位素测试精度低和两种标准物质间的δ^(18)O差值会收缩等问题进行优化试验和机理探究。创新点:首次深入探究纯培养时的溶解氧浓度和硝酸盐进样量对同位素测试结果的影响及原因,可为氧同位素测试精度的提高提供方法和参考。方法:通过控制培养瓶内的气液比(1:5、3:10、2:5和3:5)和摇床转速(60和120 r/min)来调节纯培养时的溶解氧浓度,并设计不同的硝酸盐进样量(0.05～1.00μmol),由硝酸盐标准物质的测试结果判断适宜的溶解氧浓度和硝酸盐进样量。结论:标准物质间的δ^(18)O差值收缩主要受溶解氧浓度的影响。根据氧同位素测试结果的精度和δ^(18)O差值收缩率的大小,得出以下结论:当普通三角瓶内的气液比为3:10,摇床转速为120r/min时的溶解氧浓度最佳(1.9～2.6mg/L),0.2～0.4nmol的硝酸盐进样量最适宜。
The denitrifier method is widely used as a novel pretreatment method for the determination of nitrogen and oxygen isotope ratios as it can provide quantitative and high-sensitivity measurements. Nevertheless, the method is limited by relatively low measurement accuracy for δ18 O. In this study, we analyzed the factors influencing the accuracy of δ18 O determination, and then systematically investigated the effects of dissolved oxygen concentrations and nitrate sample sizes on estimates of the δ15 N and δ18 O of nitrate reference materials. The δ18 O contraction ratio was used to represent the relationship between the measured difference and true difference between two reference materials. We obtained the following main results:(1) a gas-liquid ratio of 3:10(v/v) in ordinary triangular flasks and a shaking speed of 120 r/min produced an optimal range(1.9 to 2.6 mg/L) in the concentration of dissolved oxygen for accurately determining δ18 O, and(2) the δ18 O contraction ratio decreased as nitrate sample size decreased within a certain range(1.0 to 0.1 μmol). Our results suggested that δ18 O contraction is influenced mainly by dissolved oxygen concentrations in pure culture, and provided a model for improving the accuracy of oxygen isotope analysis.
基金
Project supported by the National Key R&D Program of China(No.2016YFD0200106)
the National Natural Science Foundation of China(No.41571450)
