Laboratory of Applied Physical Chemistry - ISOFYS, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Ghent, Belgium.
Rapid Commun Mass Spectrom. 2010 Mar;24(6):833-40. doi: 10.1002/rcm.4445.
Nitrogen (N) and oxygen (O) isotope ratios of NO(3) (-) are often used to trace dominant NO(3) (-) pollution sources in water. Both the silver nitrate (AgNO(3)) method and the bacterial denitrification method are frequently used analytical techniques to determine delta(15)N- and delta(18)O-NO(3) (-) in aqueous samples. The AgNO(3) method is applicable for freshwater and requires a concentration of 100-200 micromol of NO(3) (-) for isotope determination. The bacterial denitrification method is applicable for seawater and freshwater and for KCl extracts of soils with a NO(3) (-) concentration as low as 1 micromol. We have carried out a thorough method comparison using 42 real surface water samples having a wide range of delta(15)N- and delta(18)O-NO(3) (-) values and NO(3) (-) concentrations. Various correction pairs using three international references and blanks were used to correct raw delta(15)N- and delta(18)O-NO(3) (-) values. No significant difference between the corrected data was observed when using various correction pairs for each analytical method. Both methods also showed excellent repeatability with high intraclass correlation coefficients (ICC). The ICC of the AgNO(3) method was 0.992 for delta(15)N and 0.970 for delta(18)O. The ICC of the bacterial denitrification method was 0.995 for delta(15)N and 0.954 for delta(18)O. Moreover, a positive linear relationship with a high correlation coefficient (r >or= 0.88) between the two methods was found for delta(15)N- and delta(18)O-NO(3) (-). The comparability of the methods was assessed by the Bland-Altman technique using 95% limits of agreement. The average difference between results obtained by the bacterial denitrification and the AgNO(3) method for delta(15)N was -1.5 per thousand with 95% limits of agreement -3.6 and +0.5 per thousand. For delta(18)O this was +2.0 per thousand, with 95% limits of agreement -3.3 and +7.3 per thousand. We found that for delta(15)N and for delta(18)O, 97% of the differences fell within these 95% limits of agreement. In conclusion, the AgNO(3) and the bacterial denitrification methods are highly correlated and statistically interchangeable.
氮（N）和氧（O）同位素比值的硝酸盐（NO3-）通常用于追踪水中主要的硝酸盐（NO3-）污染源。硝酸银（AgNO3）法和细菌反硝化法是常用于测定水溶液中δ15N-和δ18O-NO3-的分析技术。AgNO3 法适用于淡水，需要 100-200 微摩尔的 NO3-用于同位素测定。细菌反硝化法适用于海水和淡水，以及 NO3-浓度低至 1 微摩尔的土壤 KCl 提取物。我们使用具有广泛的δ15N-和δ18O-NO3-值和 NO3-浓度的 42 个实际地表水样本进行了彻底的方法比较。使用三种国际参考标准和空白的各种校正对来校正原始的δ15N-和δ18O-NO3-值。对于每种分析方法，使用不同的校正对时，观察到校正后的数据之间没有显著差异。两种方法的内类相关系数（ICC）都很高，重复性也很好。AgNO3 法的 ICC 为 0.992（δ15N）和 0.970（δ18O）。细菌反硝化法的 ICC 为 0.995（δ15N）和 0.954（δ18O）。此外，发现两种方法之间存在正线性关系，相关性系数（r≥0.88）高（r≥0.88）。通过使用 95%的一致性界限的 Bland-Altman 技术评估方法的可比性。细菌反硝化法和 AgNO3 法测定δ15N的结果平均差异为-1.5‰，95%的一致性界限为-3.6‰和+0.5‰。对于δ18O，这是+2.0‰，95%的一致性界限为-3.3‰和+7.3‰。我们发现，对于δ15N 和δ18O，97%的差异在这些 95%的一致性界限内。总之，AgNO3 法和细菌反硝化法高度相关且在统计学上可互换。
