基于激光光谱分析的一种水中硝酸盐氮同位素比值测定新方法  

A New Method for Nitrogen Isotopic Analysis of Nitrate in Water by Using Laser Spectrum

作　　者：袁红朝[1] 贺珍 张丽萍[1] 耿梅梅[1] 陈闻 许丽卫[1] 李春勇[1] 彭灿 王久荣[1] YUAN Hongzhao;HE Zhen;ZHANG Liping;GENG Meimei;CHEN Wen;XU Liwei;LI Chunyong;PENG Can;WANG Jiurong(Key Laboratory of Agro-ecological Processes in Subtropical Region,Institute of Subtropical Agriculture,Chinese Academy of Sciences,Changsha 410125,China)

机构地区：[1]中国科学院亚热带农业生态过程重点实验室,湖南长沙410125

出　　处：《同位素》2022年第6期543-549,I0005,共8页Journal of Isotopes

基　　金：国家自然科学基金项目(42177330,41771334,41771337);湖南省自然科学基金面上项目(2020JJ4655);中国科学院仪器功能开发项目资助。

摘　　要：稳定同位素质谱法是氮同位素分析通用的方法之一,然而水中硝态氮同位素检测涉及的前处理方法中的化学转化法或细菌反硝化法都存在样品量消耗大、操作过程复杂,难于快速测定等问题。本研究基于稳定同位素激光光谱分析技术,结合自主研发的自动样品制备和进样前端,建立一种冷冻干燥浓缩结合化学转化N_(2)O产生法的水体硝态氮稳定同位素丰度测定方法。利用新建的方法,分析硝酸钾参比溶液和不同来源水样中硝酸盐的δ^(15)N值。结果表明,经冷冻干燥浓缩后的样品,通过制备前处理,N_(2)O产率>50%,当反应体系硝酸盐氮量在1.0~2.5μmol范围时,转化产生的N_(2)O气体浓度符合仪器检测限要求,且两种硝酸钾参比溶液均能获得较好精度,标准偏差小于0.5‰,与参比溶液的给定值基本一致,无同位素分馏(差值小于0.5‰)。对于不同来源水样中硝酸盐氮稳定同位素比值的测定也可获得较好的重现性,标准偏差小于0.5‰,且与经典质谱测定值偏差小于0.5‰。新建立的方法采用激光光谱分析,可即时得到样品的氮同位素比值,避免了传统质谱法涉及的样品气低温冷阱预浓缩过程,测试时间较质谱法快速,且操作简单,可实现纳摩尔级硝酸盐浓度的水样批量检测。Stable isotope techniques are useful to provide insights into the effects of anthropogenic disturbances on aquatic ecosystem functions.N natural abundance(expressed as the δ^(15)N value) of nitrate [NO_(3)^(-)] can provide insights into ^(15)N cycling in both aquatic and terrestrial ecosystems. Isotope ratio mass spectrometry(IRMS) is one of the most popular methods for the measurement of the nitrogen isotopic composition. However, isotope analysis of inorganic nitrogen isotopes in water has been hampered by large sample requirement, and laborious sample preparation and analyses [NO_(3)^(-)]in solutions being converted to N_(2)O by chemical conversion or bacterial denitrification methods, and then analyzed by purge-and-trap IRMS. In this study, we established a new method for nitrate-nitrogen isotope ratio analysis in water by using laser spectrum analysis system(LSAS), with an innovative equipment of interface and sample preparation device(ISPD). The LSAS is the type of quantum cascade laser absorption spectroscopy and cavity ring-down spectroscopy(CRDS) instrument using mid-infrared laser absorption spectroscopy to measure N_(2)O isotope ratios. We examined the overall performance on reference samples on varying initial [NO_(3)^(-)] concentrations, as well as the water samples from different sources. The results showed that the conversion yields for [NO_(3)^(-)] to N_(2)O was over 50% by using the auto ISPD instrument for sample preparation. The limits of quantification(LOQ) obtained from LSAS measurement was in the range of 1.0-2.5 μmol N and the gas amount was applicable for the instrument range. The δ^(15)N values for nitrate in all reference solutions and water samples were obtained with a good precision(<0.5‰) without isotope fractionation, and agreed with the results obtained by IRMS. The established LSAS method is a promising approach that can batch detection of water samples at nmol level concentration of nitrate and avoids traditional IRMS instruments pre-concentration and cryofocusing steps. It h

关 键 词：水体 硝酸盐 氮同位素 预处理 激光光谱法 

分 类 号：TL99[核科学技术—核技术及应用]