挥发性有机化合物标准样品的碳同位素δ^13C测定：以甲酸、乙酸为例

Analytical Technique of the Stable Carbon Isotope(δ^(13)C) for the Volatile Organic Compound Standard Isotopic Samples:Taking Formic and Acetic Acids for Example

密闭石英管燃烧法制备挥发性有机化合物(VOCs)标准同位素样品时,可有效避免制备过程中因挥发所导致的同位素分馏。以市售高纯度的甲酸、乙酸为标准同位素样品,重复制备它们的同位素分析样各5次,并在Finnigan MAT-252气体同位素比值质谱仪上测定其碳同位素1δ3C。结果显示此法具有极高的重现性,相对标准偏差分别为0.07%(n=5)0、.04%(n=5)。与之对比,另一套同位素测定系统(气相色谱-燃烧炉-同位素比值质谱,GC/C/IRMS)对同一标准物质的同位素测定结果并无显著差别,但在精度上却明显不及前者。密闭石英管燃烧-气体同位素质谱法的测定误差相对较小,可作为VOCs标准同位素样品的δ13C分析方法。

To avoid isotopic fractionation during the process of volatilization, we injected the volatile organic compound standard in a quartz vacuum tube which was deeped into liquid nitrogen trap, then closed it and combusted in furnace for sample preparation. Takeing marketable puriss formic and acetic acids as isotope standards, 5 repetitions were made for each and were measured on Finnigan MAT-252 mass spectrometer. The measurement results have high repeatability. The relative standard deviations of the two samples are 0.07% （n=5） and 0. 04% （n=5） respectively. Additionally,the analysis results of 5 same samples with gas chromatogram-combustion-isotope ratio mass spectrometry （GC/C/IRMS） reveal that there is no significant difference between the two methods, but the precision is less than the above mentioned. The error analysis also shows that the deviation of the analysis can be ignored, and the sealed-tube combustion method can be used to determine the δ^13C values of VOCs standards.