海水中溶解态硝酸盐的氮同位素分析的预处理方法  

Pretreatment Method for Nitrogen Isotopic Analysis of Nitrate in Seawater

作　　者：刘秀娟[1,2] 俞志明[1] 宋秀贤[1] 曹西华[1] 

机构地区：[1]中国科学院海洋研究所海洋生态与环境科学重点实验室,青岛266071 [2]中国科学院研究生院,北京100039

出　　处：《分析化学》2009年第5期643-647,共5页Chinese Journal of Analytical Chemistry

基　　金：中国科学院知识创新工程重要方向项目(Nos.KZCX3-SW-232,KZCX2-YW-208);国家基金委创新研究群体科学基金项目(No.40821004);国家863计划专题项目(No.2008AA09Z107)资助

摘　　要：建立了一套适合海水中溶解态硝酸盐的氮同位素分析的预处理方法。以蒸馏为基础,先去除海水样品中的NO2--N和NH4+-N,然后加入达氏合金将海水样品中的NO3--N还原为NH4+-N,并通过蒸馏富集,馏出液用沸石吸附后,经过滤等步骤,送入同位素质谱仪检测15N。研究了预处理过程中的蒸馏条件、盐度影响、沸石吸附效率以及大体积水样预处理方法的改进等。结果表明,每300 mL水样中加入0.5 g达氏合金在强碱性条件下蒸馏30 min,氮回收率平均可达(104.9±4.2)%(n=6);当盐度从0%增加至0.5%时,同位素分馏程度迅速减小盐度再增大时(1%～3.5%),同位素分馏变化不明显。沸石对铵氮的平均吸附率较高,约为(95.96±1.08)%(n=6);处理大体积水样时多次蒸馏并改进了馏出液的收集方式,实验效果较好。应用此方法对长江口海域水样进行了分析,结果表明,这一方法可以应用于海水中溶解态硝酸盐的氮同位素分析,为海水中溶解态氮的来源问题及循环机理研究等提供了有效信息。A suitable method for the pretreutment of dissolved nitrate samples in seawaters for nitrogen isotopic analysis was established. First, the seawater samples were processed by removing nitrite and amonium. Then Devard＇s alloy was added in sample for conversion of dissolved nitrate to ammonium. The sample was distilled, and then the ammonium condensate was collected with zeolite, after distillation, the collected condensate was filtered and prepared for determining nitropic values. Some tests of the method were conducted. The distillation condition, the influence of salinity on nitrogen isotopic analysis, absorption of ammonium onto zeolite and an improved method on a large volume of seawater were discussed in this study. The results showed that the distil- lation step had an average recovery of （104.9 ± 4.2）% （n = 6）when distillating every 300 mL aliquot of the sample under a strong alkaline condition with 0.5 g devard＇s alloy and a distillation time of 30 min. The nitrogen isotopic fractionation decreased markedly when salinity was increased from 0% to 0.5% ; further increase （1% - 3.5 % ） showed little effect. The adsorption rate of ammonium onto zeolite had a high yield of （95.96 ± 1.08） % （n = 6）in average. An improved collection method was used to process a large volume of seawater with several distillations, and had good effect on analysis. The method had been applied to analyze water samples collected from Changjiang estuary. The analytical results indicate that the method is suitable for 815N analysis of dissolved nitrate in seawaters. The present method could provide valuable information about the source and cycle mechanism of dissolved nitrogen in estuary waters.

关 键 词：海水体系 溶解态硝酸盐 稳定氮同位素分析 预处理方法 

分 类 号：P734.2[天文地球—海洋化学]