Measurement of the oxygen isotopic composition of nitrate in seawater and freshwater using the denitrifier method
Measurement of the oxygen isotopic composition of nitrate in seawater and freshwater using the denitrifier method
复制标题
DOI：
10.1021/ac020113w
复制
发表时间：
2002-10-01
影响因子：
7.4
通讯作者：
Hilkert, A
中科院分区：
文献类型：
--
作者：
Casciotti, KL;Sigman, DM;Hilkert, A
我们报告了一种测量海水和淡水中硝酸盐 (NO(3)(-)) 氧同位素组成 ((18)O/(16)O) 的新方法。反硝化器方法基于对培养反硝化细菌从硝酸盐样品中产生的一氧化二氮进行同位素比分析，该方法已在其他地方描述过，用于硝酸盐的氮同位素比 ((15)N/(14)N) 分析。(1) 在这里，我们解决了通过这种方法对硝酸盐进行 (18)O/(16)O 分析相关的其他问题，其中包括 (1) 硝酸盐样品与硝酸盐样品之间的氧同位素差异。 N(2)O 分析物是由于与硝酸盐中氧原子损失相关的同位素分馏以及 (2) 硝酸盐转化为 N(2)O 过程中氧原子与水的交换而产生的。使用 (18)O 标记水进行的实验表明，水交换对金黄色假单胞菌 N(2)O 产物中氧原子的贡献率低于 10%，通常低于 3%。此外，氧同位素分馏和氧原子交换在给定批次的分析中是一致的。因此，适当同位素参考材料的分析可用于校正测量的样品 (18)O/(16)O 比率的两种效应。这是第一个针对海水中硝酸盐 (18)O/(16)O 分析进行测试的方法。相对于已发表的淡水方法，该方法的优点包括更高的灵敏度（测试低至 10 nmol 和 1 muM NO(3)(-)）、不受其他溶质干扰以及易于样品制备。
We report a novel method for measurement of the oxygen isotopic composition ((18)O/(16)O) of nitrate (NO(3)(-)) from both seawater and freshwater. The denitrifier method, based on the isotope ratio analysis of nitrous oxide generated from sample nitrate by cultured denitrifying bacteria, has been described elsewhere for its use in nitrogen isotope ratio ((15)N/(14)N) analysis of nitrate.(1) Here, we address the additional issues associated with (18)O/(16)O analysis of nitrate by this approach, which include (1) the oxygen isotopic difference between the nitrate sample and the N(2)O analyte due to isotopic fractionation associated with the loss of oxygen atoms from nitrate and (2) the exchange of oxygen atoms with water during the conversion of nitrate to N(2)O. Experiments with (18)O-labeled water indicate that water exchange contributes less than 10%, and frequently less than 3%, of the oxygen atoms in the N(2)O product for Pseudomonas aureofaciens. In addition, both oxygen isotope fractionation and oxygen atom exchange are consistent within a given batch of analyses. The analysis of appropriate isotopic reference materials can thus be used to correct the measured (18)O/(16)O ratios of samples for both effects. This is the first method tested for (18)O/(16)O analysis of nitrate in seawater. Benefits of this method, relative to published freshwater methods, include higher sensitivity (tested down to 10 nmol and 1 muM NO(3)(-)), lack of interference by other solutes, and ease of sample preparation.