Effects of Temperature, Pressure, and Component on Raman Calibration Factores for Quantitative Measurement of Dissolved Species in Aqueous Fluid

for 11 GeoRaman International Conference, June 15-19, 2014, St. Louis, Missouri, USA EFFECTS OF TEMPERATURE, PRESSURE, AND COMPONENT ON RAMAN CALIBRATION FACTORES FOR QUANTITATIVE MEASUREMENT OF DISSOLVED SPECIES IN AQUEOUS FLUID Wanjun Lu 1 , Qingcheng Hu 2 , Wenjia Ou 3 , Ying Chen 4 , Yiqi Huang 5 1 State Key Laboratory of Geological Processes and Mineral Resources(GPMR), Faculty of Mineral Resources (FMR), China University of Geosciences (CUG), Lumo Road NO.388, Wuhan, China ([email protected]), 2 FMR, CUG ([email protected]), 3 FMR, CUG ([email protected]), 4 School of Environmental Studies, CUG ([email protected]), 5 School of Environmental Studies, CUG ([email protected]) Introduction: Raman spectroscopy has been proved to be a promising method for quantitatively studying fluid inclusions [1-3] for its high sensitivity and non-destructivity. However, to quantitatively measure abundance of components of interest needs a suitable and stable species as the internal standard, and calibration of relationship between Raman quantitative factors and concentrations of components is further required under wide range of temperature and pressure conditions covered by fluid inclusions [4]. It has been proved by some previous work that Raman quantitative factors could be remarkably modified by temperature and vary from one species to another [5, 6]. However, accurate calibration data of component analysis for fluid inclusions are poorly available under wide range of P, T conditions. In this paper, changes of Raman quantitative parameters with varying temperature, pressure, and component are discussed based on investigating Raman spectra of CO2, CH4, and Na2SO4 aqueous solutions with different concentrations of solutes under wide range of temperatures and pressures. The cases selecting different internal reference with respect to water, SO4 2are also compared. Methods: A series of experiments were carried in the capillary high-pressure optical cell (HPOC; [7]) in combination with a Linkam CAP500 heating-cooling stage where the temperature was read with accuracy of ±0.1 o C. The pressure was measured with accuracy of ±0.14%. More details could be found elsewhere [8] . Three kinds of systems were prepared: Na2SO4 aqueous solutions, homogeneous CO2-(NaCl-)H2O solutions and CH4-H2O solutions. The procedure for preparing these solutions was reported elsewhere [4] Results and discussion: Using Raman intensity ratio as the calibration parameter Raman calibration for determining concentration of CO2 in pure water was derived by constructing relationship between peak intensity ratio Ir,CO2 (the vu of CO2 Fermi dyad at ~1385 cm -1 to the OH stretching vibration (vw) of water in CO2 homogeneous solutions) and temperature (T=0-300 oC). As depicted by Figure 1, Ir,CO2 shows different dependence-behavior on T in NaCl solutions with different concentrations of NaCl. It was further illustrated that pressure has negligible effect on Ir,CO2. Figure 1. Comparison among relationships of Ir,CO2 and temperature in different concentrated NaCl solutions. Figure 2. Comparison of dependence of Ir,Na2SO4 on temperature in different concentrated Na2SO4 solutions. Intensity ratio of Raman peak for SO4 2at ~965 cm -1 and vw (Ir,Na2SO4) also exhibits different dependance behaviors on temperature among solutions with different concentrations of Na2SO4, likely by a contrary way to the case for CO2-(NaCl-)H2O solutions (Figure 2). This phenomenon is considered to be closely related to the deformed Raman contours for O-H stretching vibration of water by temperature and salinity of solutions. On the other hand, different modification effects of electrolytes on structure of water (struc5076.pdf 11th International GeoRaman Conference (2014)