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三价钛还原法分析硝酸根氮氧同位素的方法研究
杨海丽
0
(自然资源部第三海洋研究所,福建 厦门 361005)
摘要:
本研究利用三价钛还原法将标准样品、海水、湖水和雨水中硝酸根转化为N2O测试其氮氧同位素值,并优化实验条件(NO-3浓度、试剂量、反应时间和温度等)。结果表明:4 cm3硝酸根水样(浓度约为20 μmol/dm3),加入100 mm3TiCl3溶液(浓度为150 g/dm3),25 ℃反应24 h,NO-3还原为N2O的平均转化率为86.3%(n=5)。5种丰度硝酸根氮氧同位素标样校准曲线斜率分别为0.947和0.617,相关系数R2分别为0.999和0.994;方法检出限的NO-3浓度为2.5 μmol/dm3,其δ15N的标准偏差小于0.7‰(n=5),δ18OVSMOW值的标准偏差小于2.5‰(n=5);20 μmol/dm3硝酸根样品δ15N的标准偏差小于0.5‰(n=5),δ18OVSMOW值的标准偏差小于1.0‰(n=5)。该方法测定3种不同类型水样δ15N的标准偏差分别为0.3‰、0.6‰和0.5‰;δ18OVSMOW的标准偏差分别为2.1‰、2.0‰和1.6‰。三价钛还原法分析水体中硝酸根氮氧同位素操作步骤简单,测试效率高,但氧同位素结果需要系统校正。
关键词:  海洋化学  三价钛还原法  氮同位素  氧同位素  硝酸根  N2O
DOI:10.3969/J.ISSN.2095-4972.20221126001
基金项目:国家自然科学基金(42176057,41976050)
Determination of the nitrogen and oxygen isotopic composition of dissolved nitrate by Ti3+reduction method
YANG Haili
(Third Institute of Oceanography, MNR, Xiamen 361005, China)
Abstract:
This study uses the trivalent titanium reduction method to convert nitrate ions in standard samples of seawater, lake water, and rainwater into N2O to test their nitrogen and oxygen isotope values, and optimize experimental conditions (NO-3 concentration, reagent amount, reaction time, and temperature, etc.). Results show that when 4 cm3 nitrate water sample with concentration approximately 20 μmol/dm3, added with 100 mm3 TiCl3 solution 150 g/dm3 and reacted at 25 ℃ for 24 hours, the average conversion rate of NO-3 reduction to N2O is 86.3% (n=5). The slopes of the calibration curves for 5 nitrate nitrogen and oxygen isotope standards are 0.947 and 0.617, respectively, and the correlation coefficients R2 are 0.999 and 0.994, respectively. The detection limit of the method is 2.5 μmol/dm3 for NO-3, of which the standard deviation of δ15N is less than 0.7‰ (n=5), the standard deviation of δ18OVSMOW value is less than 2.5‰ (n=5), standard deviation of δ15N is less than 0.5‰ (n=5), and standard deviation of δ18OVSMOW value is less than 1 ‰ (n=5). Thus, three types of water samples measured by the method have resulted in standard deviation of 0.3 ‰, 0.6‰, and 0.5‰ for δ15N, respectively and standard deviations of 2.1‰, 2.0‰ and 1.6‰ for δ18OVSMOW, respectively. The Ti3+ reduction method is simple and efficient for the determination of nitrogen and oxygen isotope of NO-3 in water, but the oxygen value needs to be corrected systematically.
Key words:  marine chemistry  Ti3+reduction method  nitrogen isotope  oxygen isotope  nitrate  nitrous oxide

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