分流比对烃类单分子氢同位素分析的影响
Effect of Split Ratio on Hydrogen Isotope Ratio Analysis for the Single Molecule Hydrocarbons
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摘要: 在单体烃的氢同位素系统测定中,以甲烷为样品,选择不同的分流比(0.1、0.5、1.0、2.0、5.0、10.0),采用气相色谱-高温热转换-同位素比率质谱对相应的氢同位素比值进行研究。结果表明,不同的分流比对峰形、出峰面积及单体烃的氢同位素值有不同程度的影响,总体上随着分流比的增大,峰宽及峰面积呈现指数方式递减;特别是当分流比较小(小于1)时,导致氢同位素值测定结果的不确定度增大;分流比较大时,氢同位素值趋于稳定。文章对造成这种现象的原因进行了分析,认为在单体烃的氢同位素的分析中,选择较大的分流比不会导致明显的同位素分馏,从而对样品分析更为有利。Abstract: In hydrogen isotope ratio analysis of single molecule hydrocarbons by gas chromatography-high temperature thermal conversion-isotope ratio mass spectrometry, different split ratios (0.1, 0.5, 1.0, 2.0, 5.0 and 10.0)were selected to study the corresponding hydrogen isotope ratios. The results showed that different inlet split ratios influenced in various extents on the peak area and peak width, namely, the peak area and peak width decreased exponentially with the increase of split ratios. Especially when split ratios were less than 1.0, the uncertainty of the hydrogen isotope determination results increased. And when the split ratios were relatively larger, hydrocarbon isotope determination results became stable. The reasons for this phenomenon were also discussed. The research results also showed that in the hydrogen isotope analysis, the choice of a larger split ratio did not lead to significant isotopic fractionation and was more favorable for the sample analysis.
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