~(15)N示踪-质谱计法直接定量稻田土壤反硝化作用氮素损失的可行性研究

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。

STUDIES ON THE FEASIBILITY OF DIRECT MEASUREMENT OF N LOSSES AS N_2 AND N_2O PRODUCED BY DENITRIFICATION WITH ~(15)N TRACER TECHNIQUE AND MASS SPECTROMETER

With 15 N tracer technique, mass spectrometer and a self\|designed installation including sample entrance, reduced Cu tube, high\|efficiency O\-2 trap, liquid N\-2 cold trap, a method for direct determination of N losses as N\-2 and N\-2O produced by denitrification is set up.The average of 15 N natural abundance of atmospheric samples determined is 0\^3659%(the theoretical value is 0\^3660%) with C.V.% of 0\^09% and an average of absolute error of 0\^0002%, which is up to the error standard of the mass spectrometer used. C.V.% of measurement of 15 N abundance in different gas samples and in the substrate NO\+\+-\-\-3 undergoing denitrification are 0\^03%～1 08% and 1\^22%～5\^21%,respectively,indicating that the pretreating installation is highly efficient for elimination of O\-2, CO\-2 and H\-2O in gas samples, and the method is feasible for direct measurement of 15 N losses as N\-2 and N\-2O. As the calculation of 15 N losses is based on atom excess % of 15 N( 15 N abundance of gas sample minus 15 N natural abundance of atmospheric N\-2), C.V.% of determination of 15 N losses is probably larger than 5% if atom excess % of 15 N in gas samples is smaller than 0\^014%. It is suggested that the 15 N abundance higher than 0\^380% in gas samples be suitable.