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The impacts of elevated temperature and mNaCl for in situ Raman quantitative calibration of dissolved gas species
Chemical Geology ( IF 3.9 ) Pub Date : 2021-08-17 , DOI: 10.1016/j.chemgeo.2021.120490
Lianfu Li 1, 2 , Xin Zhang 1, 2, 3 , Zhendong Luan 1, 2 , Zengfeng Du 1 , Shichuan Xi 1, 3 , Jun Yan 1
Affiliation  

In the past ten years, Raman spectroscopy analysis has been widely applied to the quantification of the components of hydrothermal fluids and fluid inclusions. However, the accuracy of the quantitative results of Raman spectroscopy is highly dependent on the quantitative calibration model. How temperature and salinity affect quantitative calibration models remains an unsolved question, which severely hinders the accurate geochemical characterization of hydrothermal fluids and fluid inclusions. In this study, the Raman spectra of the symmetric stretching mode of methane (~ 2917 cm−1) in homogeneous CH4-containing aqueous solutions were obtained at temperatures from 25 to 300 °C, pressures from 0.1 to 40 MPa, and mNaCl from 0 to 5.0 mol/kg to research the effects of elevated temperature and salinity on the Raman spectroscopy quantitative measurement of gas species, and two Raman calibration models of CH4 that reference OH bending and stretching bands were established. Both models show high dependence on salinity. Large measurement errors, causing underestimation of methane concentrations by up to 57.5%, occur if the salinity of the fluids is not taken into account during the calibration. The contributions of the Raman scattering cross section (RSCS) and molar density to the change of quantification factors (QFs) were quantified, and the results showed that the variation of the RSCS is the main factor determining QF values. The significant discrepancy between the measured and predicted QFs demonstrates that changes in the peak areas of both H2O and CH4 contribute to the dependence of quantitative calibration models on temperature and salinity.



中文翻译:

高温和mNaCl对溶解气体物种原位拉曼定量校准的影响

近十年来,拉曼光谱分析已广泛应用于热液和流体包裹体成分的定量分析。然而,拉曼光谱定量结果的准确性高度依赖于定量校准模型。温度和盐度如何影响定量校准模型仍然是一个悬而未决的问题,这严重阻碍了热液流体和流体包裹体的准确地球化学表征。在这项研究中,对称的拉曼光谱拉伸甲烷的模式(〜2917厘米-1)在均相CH 4在温度获得从25至300℃的含水溶液,压力为0.1〜40兆帕,和NaCl 0~5.0 mol/kg,研究升高温度和盐度对气体种类拉曼光谱定量测量的影响,并建立了两个参考OH弯曲和拉伸带的CH 4拉曼校准模型。两种模型都表现出对盐度的高度依赖。如果在校准过程中不考虑流体的盐度,则会出现较大的测量误差,导致甲烷浓度低估高达 57.5%。量化了拉曼散射截面(RSCS)和摩尔密度对量化因子(QF s)变化的贡献,结果表明RSCS的变化是决定QF的主要因素值。测量的和预测的QF s之间的显着差异表明 H 2 O 和 CH 4峰面积的变化导致定量校准模型对温度和盐度的依赖性。

更新日期:2021-08-17
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