Analytical Chemistry 文章：
Combining Denitrifying Bacteria and Laser Spectroscopy for Isotopic Analyses (δ15N, δ18O) of Dissolved Nitrate
通過反硝化細菌和激光同位素分析儀測定溶解硝酸鹽中的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.
關于水中硝酸鹽樣品δ15N和δ18O的同位素測量，我們提出一種創新的革命性方法：利用反硝化細菌培養轉化產生的N2O和離軸積分腔輸出光譜技術(簡稱：OA-ICOS技術)。對于測量溶解的硝酸鹽樣品，將頂空搜集的N2O氣體樣品，用進樣針注入到一個基于OA-ICOS技術的N2O激光同位素分析儀，手動進樣口有隔膜密封，樣品分析時間：300秒。這種OA-ICOS技術可以獲得高精度及高準確度的δ15N和δ18O同位素比值結果。
這種新的同位素分析技術與傳統同位素分析手段相比具有如下優點：
1.在不需要預濃縮的情況下，提供δ15N 和 δ18O同位素比值的精確測量;
2.消除其它氣體的干擾，如水和二氧化碳;
3. 與同位素質譜儀相比，節省了大量的成本和維護費用。
這種方法將大大簡化水系統中的硝酸鹽來源的鑒定和定量工作。
