元素分析-同位素质谱测定δ^(15)N和δ^(34)S的信号强度响应特征

Effect of Sample Signal Intensity onδ^(15)N andδ^(34)S Measurement by EA-IRMS System

自然界中不同类型样品C、N和S元素含量以及C/N和C/S的差异极大,导致元素分析-同位素比值质谱仪(EA-IRMS)联机系统的进样量和检测信号强度的变化范围极大。进样量和信号强度对EA-IRMS测定δ^(15)N和δ^(34)S的影响将导致样品测量结果具有较大的不确定性。为应对样品中目标元素含量低或样品稀缺等限制,本研究重点关注EA-IRMS测定δ^(15)N和δ^(34)S的信号强度依赖性特征。结果表明,EA-IRMS在小元素进样量或弱信号强度条件下测定δ^(15)N和δ^(34)S需要进行空白校正。在1.71~561.93μg N和3.74~100.62μg S的进样条件下,同位素标准物质δ^(15)N和δ^(34)S的测定误差变化范围分别为0.18‰~0.54‰和0.21‰~0.88‰,测定精度变化范围分别为0.24‰~0.57‰和0.27‰~0.54‰。该联机系统对高C/N和C/S(>200)木材标准物质测定时,其δ^(15)N平均误差为0.34‰,其δ^(34)S的测定精度为0.58‰。此外,对两种木材样品δ^(15)N的连续(6~20 d)测定证明该联机系统的测定结果具有较好的时间稳定性。该研究可为EA-IRMS技术的应用与发展提供数据参考。

Carbon-nitrogen ratio(C/N)and carbon-sulphur ratio(C/S)of unknown samples can vary greatly in the natural environment.There are also distinct differences in the ionization efficiencies of N and S elements.These factors will introduce the fluctuation of signal intensity to the element analysis-isotope ratio mass spectrometry(EA-IRMS),which can has a further impact on the measurements of sampleδ^(15)N andδ^(34)S.However,the analysis of unknown sampleδ^(15)N andδ^(34)S is always restricted by the low content or the scarcity of the target elements.In this study,we focused on the effect of sample amount and signal intensity on theδ^(15)N andδ^(34)S measurement by EA-IRMS.Our results indicated that the EA-IRMS measurement ofδ^(15)N andδ^(34)S was significantly affected by the“blank effect”when the sample amount and signal intensity were limited during the mass spectrometry analysis.Under the injection conditions of 1.71-561.93μg N and 3.74-100.62μg S,the variation ranges of the measurement errors of the isotopic reference materialsδ^(15)N andδ^(34)S were 0.18‰-0.54‰and 0.21‰-0.88‰,respectively.Meanwhile,the variation ranges of the measurement errors of measurement precision were 0.24‰-0.57‰and 0.27‰-0.54‰,respectively.With the high C/N and C/S wood samples,the measurement errors of EA-IRMS were 0.34%forδ^(15)N.Because the true value of the above wood sampleδ^(34)S was unknown,the measurement precision of EA-IRMS on the wood samples was 0.58‰.Based on the analysis of two wood sampleδ^(15)N,the EA-IRMS had a good time stability during the continuous(6-20 days)measurement process.We hoped these findings could provide implications for the application of EA-IRMS in biogeochemistry and life science areas.