N2-CH4（CO2）混合气体在线标样制备及其拉曼定量因子测定

利用混合气体的标准样品对激光拉曼探针进行标定,可以快速准确地对包裹体中的无机及有机气相组分进行定量分析。而常用的商用钢瓶装混合气体标样,存在费用高、气体组成单一固定等缺点。本文设计了一套在线标样制备装置,提出一种在线配置不同浓度和压力条件下混合气体标样的方法。利用高纯度(纯度99.999%)的N2、CH4以及CO2钢瓶气,经过在线混合增压,在5 MPa和10 MPa条件下制备了N2摩尔分数为30%、50%和70%的N2-CH4以及N2-CO2混合气体在线标样。该方法制备的标样与70%N2+30%CO2的商用钢瓶气标样对比表明,CO2与N2的拉曼相对峰高以及相对峰面积值的误差在4%以内,具有较高的准确度和重现性。通过不同压力和浓度条件下CH4以及CO2的拉曼相对定量因子测定表明,气体的相对定量因子在5~10 MPa压力条件下与压力及组成无关。地质样品应用结果表明,本方法可以方便、灵活、准确地按任意比例将两瓶及两瓶以上纯气体钢瓶样品进行混合及增压,为激光拉曼标定、气体组成原位测量等提供了一种新的技术思路。

Synthesis of N2-CH4 and N2-CO2 Gas Mixtures as an Online Standard and Determination of Their Raman Quantification Factors of CH4 and CO2

Organic and/or inorganic gas composition can be measured quickly and accurately by using a Laser Raman Microprobe with an online standard of gas mixtures. The accuracy of the standard sample plays an important role in this method, but the commercial standard mixed gas cylinders are expensive with fixed composition that cannot be modified arbitrarily. A new method to synthesize the gas mixtures in different compositions under different pressures has been developed. The N₂-CH₄ and N₂-CO₂ gas mixtures with varied N₂ mol contents of 30%, 50% and 70% were synthesized. The pressure of these gas mixtures were increased to 5 and 10 MPa. Both the synthesized and commercial gas mixtures of 70% N₂ and 30% CO₂ have similar relative peak heights and peak areas of N₂ and CO₂. The error of this method is less than 4%. The Raman quantification factor of CH₄ and CO₂ are determined. In this study, the Raman quantification factor is insensitive to composition and pressure under 5 MPa and 10 MPa. This new method is relatively simple, easy and accurate, and only two or more kinds of pure gas cylinders are used to synthesize gas mixtures with different composition and under different pressure, which provides a new way for laser Raman calibration and gas composition measurement in situ.