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采用自行设计的气样前处理装置 ,包括进样口、还原铜管、高效脱氧管和液氮冷阱 ,建立了1 5N示踪 质谱计法直接测定反硝化作用气态氮素损失 (N2 +N2 O)的方法。测得空气中N2 的1 5N自然丰度平均为 0 36 5 9% (理论值为 0 36 6 0 % )、绝对误差的平均值为 0 0 0 0 2 %、C V %为 0 0 9% ,与质谱计的设计精度完全吻合 ;不同气样1 5N丰度测定的C V %在 0 0 3%～ 1 0 8%之间 ,反硝化作用源丰度测定的C V %在 1 2 2 %～ 5 2 1 %之间 ,表明本研究所用的前处理装置对气样中O2 、CO2 及H2 O等杂质气态的清除是十分有效的。另一方面 ,由于1 5N损失的计算是以1 5N原子百分超为基础的 ,计算结果表明 ,当气样的1 5N原子百分超小于 0 0 1 4% (相应的1 5N丰度为 0 380 % )时 ,测得的1 5N损失的C V %有可能大于 5 % ,为此建议气样1 5N丰度最好能大于 0 380 % ,以确保测定结果的精确度。
A 15 N tracer mass spectrometer was established for the direct determination of the gaseous nitrogen loss by denitrification (N2 + N2) using a self-designed gas sample pretreatment device including an inlet, a reducing copper tube, an efficient deoxygenation tube and a liquid nitrogen cold trap. O) method. The average natural abundance of 15N in air was 0 36 5 9% (theoretical value 0 36 6 0%). The absolute value of absolute error was 0 0 0 0 2% and the CV% was 0 0 9% Which is in good agreement with the design accuracy of the mass spectrometer. The CV% of the abundance of 15N in different gas samples was between 0 0 3% and 1 0 8%, and the CV% of the denitrification abundance was between 122% and 5% 21%, indicating that the pretreatment device used in this study is very effective in removing gaseous impurities such as O 2, CO 2 and H 2 O from the gas sample. On the other hand, since the loss of 15N is calculated on the basis of 15N atomic percent, the calculation results show that when the atomic percentage of the gas sample is less than 1004% (the corresponding abundance of 15N is 0 380%), the measured CV% of 1 5N loss may be more than 5%. Therefore, it is suggested that the abundance of 1 5N should be greater than 0 380% in order to ensure the accuracy of the determination result.