Analytical Chemistry 文章：
Combining Denitrifying Bacteria and Laser Spectroscopy for Isotopic Analyses (δ15N, δ18O) of Dissolved Nitrate
通过反硝化细菌和激光同位素分析仪测定溶解硝酸盐中的δ15N和δ18O
David X. Soto *?, Geoff Koehler ?, and Keith A. Hobson ?
? Environment Canada, 11 Innovation Boulevard, Saskatoon, Saskatchewan, Canada, S7N 3H5
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Abstract
We present a novel approach for nitrogen (δ15N) and oxygen (δ18O) isotopic analysis of nitrate in water based on the isotopic analysis of N2O produced from the conversion of NO3– by cultured denitrifying bacteria and off-axis integrated cavity output spectroscopy (OA-ICOS). The headspace N2O was manually injected into an OA-ICOS isotopic N2O laser analyzer through a syringe septum port. Sample analysis time was ～300 s. The use of OA-ICOS technology yields accurate and precise δ15N and δ18O results for dissolved nitrate samples when nonlinearity issues are considered. This new isotope analytical technique thus improves the isotopic analysis of nitrates by (i) providing accurate measurements of δ15N and δ18O without preconcentration, (ii) eliminating interferences by other gas substances (i.e., H2O and CO2), and (iii) reducing extensive maintenance and costs of isotope ratio mass spectrometers (IRMS). This approach will greatly streamline the identification and quantification of nitrate sources in aquatic systems.
关于水中硝酸盐样品δ15N和δ18O的同位素测量，我们提出一种创新的革命性方法：利用反硝化细菌培养转化产生的N2O和离轴积分腔输出光谱技术(简称：OA-ICOS技术)。对于测量溶解的硝酸盐样品，将顶空搜集的N2O气体样品，用进样针注入到一个基于OA-ICOS技术的N2O激光同位素分析仪，手动进样口有隔膜密封，样品分析时间：300秒。这种OA-ICOS技术可以获得高精度及高准确度的δ15N和δ18O同位素比值结果。
这种新的同位素分析技术与传统同位素分析手段相比具有如下优点：
1.在不需要预浓缩的情况下，提供δ15N 和 δ18O同位素比值的精确测量;
2.消除其它气体的干扰，如水和二氧化碳;
3. 与同位素质谱仪相比，节省了大量的成本和维护费用。
这种方法将大大简化水系统中的硝酸盐来源的鉴定和定量工作。
