土壤硝酸盐中15N同位素测定前处理自动化辅助装置设计和验证

随着稳定同位素质谱技术在土壤氮循环研究中的广泛应用,氮稳定同位素分析对样品前处理方法提出了更高要求,而合适的样品处理方法是确保分析结果准确可靠的关键。设计开发1种适用于土壤微量硝酸盐中氮稳定同位素分析前处理辅助装置,将基于光电感应装置的自动进样系统与注液、抽真空-气体置换系统相融合,将原前处理方法中液体试剂注入,反应体系抽真空及氦气置换等人为操作过程改为自动化处理环节。系统测试结果表明:该套辅助装置具有良好的自动抽真空、注气和加液重复性。装置抽真空系统的真空度绝对误差可控制在0.5 Pa以内,气体注入体积绝对误差可控制在0.2 mL以内,而注液系统的注液体积绝对误差也可控制在0.1 mL以内,变异系数(CV)均小于1%。使用标准参比样品测试整套系统的准确度和精密度,所有测试样品均获得了较好的准确度和精密度,CV<1%。研制的装置结合痕量气体预浓缩装置—稳定同位素质谱(PreCon-IRMS)联用仪,可以建立方便快捷的低样品量下硝酸盐中15 N同位素质谱检测方法,可为土壤氮循环过程研究提供关键技术支撑。

Design and Test of Automatic Pretreatment Auxiliary Device for15N Isotope Analysis of Soil Nitrate

With the application of stable isotope mass spectrometry in soil nitrogen cycle research, nitrogen stable isotope analysis puts higher requirements for the sample pretreatment methods. At the same time, a suitable pretreatment process is also the guarantee of the analysis result accuracy. A automatic pretreatment auxiliary device for nitrogen stable isotope analysis of soil nitrate is designed and developed in this paper. The auto-injection system based on photoelectric sensing device is integrated with the liquid injection and vacuum-gas replacement system to achieve automatic process instead of manual operation, ie., liquid reagent injection, vacuum extraction of reaction system, helium gas displacement and other artificial processes. The results of system test showed that the device has a good vacuum, gas injection and liquid repeatability. The absolute error of the system vacuum degree, gas injection volume and the liquid injection system of the device can be controlled within 0.5 Pa, 0.2 mL, and 0.1 mL respectively, with CV< 1%. The accuracy and precision of the entire system were also tested by using standard reference samples. All test samples obtained good accuracy and precision of 0.1%~0.6% with CV<1%. The developed device combined with the trace gas preconcentration device-stable isotope mass spectrometry instrument (PreCon-IRMS) can establish a convenient and rapid method for the nitrogen stable isotope determination of nitrate at low sample volume, which can provide a key technical support for soil nitrogen cycle process research.