Sensitive determinations of stable nitrogen isotopic composition of organic nitrogen through chemical conversion into N2O
Sensitive determinations of stable nitrogen isotopic composition of organic nitrogen through chemical conversion into N2O
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DOI：
10.1002/rcm.3368
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发表时间：
2008-01-01
影响因子：
2
通讯作者：
Nakagawa, Fumiko
中科院分区：
文献类型：
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作者：
Tsunogai, Urumu;Kido, Tadasuke;Nakagawa, Fumiko
我们提出了一种对海水和淡水中颗粒有机氮 (PON) 进行高灵敏度氮同位素分析的方法，目的是通过 N-15(2) 示踪技术测定含有低丰度生物体的样品的水生固氮率。该方法由传统的氧化/还原方法组成，例如使用过硫酸盐将PON氧化为硝酸盐（NO3），使用海绵镉将NO3还原为亚硝酸盐（NO2），以及使用叠氮化钠进一步将NO2还原为一氧化二氮（N2O）。然后，从水中清除 N2O，并低温捕获，随后释放到气相色谱柱中，通过同时监测质量 30,31 和 32 处的 NO+ 离子流，使用连续流同位素比质谱 (CF-IRMS) 分析稳定的氮同位素组成。每批分析中的氮同位素分馏都是一致的。样品测量的标准偏差小于0.3%。对于含有 PON 超过 50 nmolN 的样品，对于超过 20 nmolN 的样品，为千分之 0.5，通过减去空白氮的贡献，最终 N2O 为 8 +/- 2 nmol。通过使用这种方法，我们可以比其他方法更好地测定少量 PON 的 delta N-15，因此我们可以减少孵育以确定固氮率所需的水样数量。此外，我们还可以通过将该方法应用于滤液来扩展该方法，以确定一般有机氮的氮同位素组成，例如总溶解氮（TDN；NO3、NO2、铵和DON的总和）的氮同位素组成。版权所有 (c) 2008 John Wiley & Sons, Ltd.
We present a method for high-sensitivity nitrogen isotopic analysis of particulate organic nitrogen (PON) in seawater and freshwater, for the purpose of determining the aquatic nitrogen fixation rate through the N-15(2) tracer technique for samples that contain a low abundance of organisms. The method is composed of the traditional oxidation/reduction methods, such as the oxidation of PON to nitrate (NO3) using persulfate, the reduction of NO3 to nitrite (NO2) using spongy cadmium, and further reduction of NO2 to nitrous oxide (N2O) using sodium azide. Then, N2O is purged from the water and trapped cryogenically with subsequent release into a gas chromatography column to analyze the stable nitrogen isotopic composition using continuous-flow isotope ratio mass spectrometry (CF-IRMS) by simultaneously monitoring the NO+ ion currents at masses 30,31, and 32. The nitrogen isotopic fractionation was consistent within each batch of analysis. The standard deviation of sample measurements was less than 0.3%. for samples containing PON of more than 50 nmolN, and 0.5 parts per thousand for those of more than 20 nmolN, by subtracting the contribution of blank nitrogen, 8 +/- 2 nmol at final N2O. By using this method, we can determine delta N-15 for lower quantities of PON better than by other methods, so we can reduce the quantities of water samples needed for incubation to determine the nitrogen fixation rate. In addition, we can expand the method to determine the nitrogen isotopic composition of organic nitrogen in general, such as that of total dissolved nitrogen (TDN; sum of NO3, NO2, ammonium, and DON), by applying the method to filtrates. Copyright (c) 2008 John Wiley & Sons, Ltd.