显微激光拉曼定量分析CO_2气体碳同位素组成方法研究

Research on Quantitative Method for the Determination of Carbon Isotopic Composition of CO_2 with Micro-Laser Raman Spectroscopy

制备了一系列不同比例的^(12)CO_2/N_2和^(13)CO_2/N_2混合物,对样品进行显微激光拉曼测试分析后发现气体拉曼特征峰峰面积比与其摩尔分数比成正比例关系,拟合方程的斜率被认为是拉曼量化因子F_(12CO_2)和F_(13CO_2)。用气相组分中只含有^(12)CO_2和N_2的流体包裹体验证了当F_(12CO_2),为1.163 49时,根据气体的拉曼特征峰峰面积比能估算出其摩尔分数比。由线性拟合后的方程斜率得出F_(13CO_2)和F_(12CO_2)分别为1.610 86和1.163 49,它们的比率F_(13CO_2)/F_(12CO_2)是1.3845。在确定稳定同位素分子的拉曼参数和实验条件基础上,CO_2气体碳同位素摩尔分数比C_(12)/C_(13)可根据A_(12Co_2)/A_(13CO_2)(拉曼峰峰面积比)和F_(13CO_2)/F_(12CO_2)的乘积求出。此外,用已知摩尔分数比(C_(12)/C_(13))的人造包裹体验证了此方法具有一定的可行性,可以建立起定量分析CO_2气体碳同位素激光拉曼测试方法。

In this study,a series of ^12CO2/N2 and ^13CO2/N2 binary mixtures with various molar fraction ratios were synthesized.It was found that the Raman peak area ratios were proportional to molar fraction ratios.The linearity of the working curves was very good.Moreover,the slopes of working curves were regarded as Raman quantification factor（F12CO2 and F13CO2.The natural fluids only containing ^12CO2 and N2 composition in the gas phase have been applied to estimate their molar fraction ratios when F12CO2 is 1.163 49.As F13CO2 and F12CO2 are equal to 1.610 86 and 1.163 49,their ratio（F13CO2 /F12CO2） is 1.384 5.Based on the study of principles and feasibility of the method of laser Raman spectroscopy,the molar fraction ratio C12/C13 would be calculated using the product of A12CO2 /A13CO2（the ratio of Raman peak area） and F13CO2 /F12CO2.In addition,man-made inclusions with known molar fraction ratios（C12 /C13） were presented to testify the validity and precision of the method.The possibility of quantifying carbon isotopic composition of CO2 with Micro-Laser Raman Spectroscopy is demonstrated.