RATIONALE The recently reported acetone method for δ15 N-NO3 - analysis is a straightforward sample preparation process. However, the applicability of the method to water samples having high salinity and low concentration of nitrates is not good. Therefore, we developed a new method to measure δ15 N-NO3 - values in a saline sample having low nitrate concentration by improving the acetone method (the adapted method), and verified its usability. METHODS The adapted method involves (a) reducing a large volume of sample by evaporation, (b) removing NaCl by mixing acetone twice, (c) changing the volume ratio of the acetone/NaI/n-hexane solvent from 21/0.35/10 to 30/0.25/5 mL, (d) using an increased volume of BaI2 (0.1 M) - from 0.75 to 1 mL, and (e) using an alternative capsule drying process of lyophilization. RESULTS The adapted method has provided nearly exact δ15 N-NO3 - values of standard materials with high precision and accuracy (<0.1‰) at a lower cutoff of 2 μmol of NO3 - in a sample capsule. The recovery of NO3 - in this method was significantly dependent (P < 0.05) on the Cl- concentration of the samples. However, a minimum recovery of 60% NO3 - , required for the reproducibility of the accurate value of δ15 N-NO3 - , was possible from the concentrated sample aliquot containing up to 6 g of Cl- . The application of the adapted acetone method to creek water samples, collected from mangrove watersheds, has shown high consistency in the analysis results. CONCLUSIONS It was proved that the inexpensive and easy-to-handle adapted acetone method could be used for the δ15 N-NO3 - analysis of saline water samples when the sample aliquot contained about 4 μmol of NO3 - with less than 6 g of Cl- .

中文翻译：

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丙酮方法适用于δ15N-NO3-分析低硝酸盐浓度的盐水。

理由最近报道的用于δ15N-NO3的丙酮分析方法是一种简单的样品制备过程。然而，该方法对具有高盐度和低硝酸盐浓度的水样品的适用性不好。因此，我们开发了一种通过改进丙酮法（改进的方法）来测量硝酸盐浓度较低的盐溶液中δ15N-NO3-值的新方法，并验证了其可用性。方法调整后的方法包括（a）通过蒸发减少大量样品;（b）通过将丙酮混合两次除去NaCl;（c）将丙酮/ NaI /正己烷溶剂的体积比从21 / 0.35 / 10更改为到30 / 0.25 / 5 mL，（d）使用增加体积的BaI2（0.1 M）-从0.75到1 mL，以及（e）使用冻干的另一种胶囊干燥工艺。结果改进后的方法在样品胶囊中提供了几乎精确的δ15N-NO3-标准材料的值，具有较高的精确度和准确度（<0.1‰），且NO2的下限较低。在此方法中，NO3-的回收率显着依赖于样品的Cl-浓度（P <0.05）。但是，从含有多达6 g Cl-的浓缩样品等分试样中，可以实现δ15N-NO3-准确值的再现性所需的最低60％NO3-的回收率。自适应丙酮方法在从红树林流域收集的小溪水样中的应用在分析结果中显示出高度的一致性。