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This work aims to quantify sulfate ion concentrations in the system Na_2SO_4-H_2O using Raman micro-spectroscopy.Raman spectra of sodium sulfate solutions with known concentrations were collected at ambient temperature(293 K) and in the 500 cm~(_1)-4000 cm~(-1) spectral region.The results indicate that the intensity of the SO_4~(2-) band increases with increasing concentrations of sulfate ion.A linear correlation was found between the concentration of SO_4~(2-)(c) and parameter I_1,which represents the ratio of the area of the SO_4~(2-) band to that of the O-H stretching band of water(A_s/A_w):I_1=-0.00102+0.01538 c.Furthermore,we deconvoluted the O-H stretching band of water(2800 cm~(-1)-3800 cm~(-1)) at 3232 and 3430 cm~(-1) into two sub-Gaussian bands,and then defined Raman intensity of the two sub-bands as A_(Bi)(3232 cm~(-1)) and A_(B2)(3430 cm~(-1)),defined the full width of half maximum(FWHM) of the two sub-bands as W_(B1)(3232 cm~(-1)) and W_(B2)(3430 cm~(-1)).A linear correlation between the concentration of SO_4~(2-)(c) and parameter I_2,which represents the ratio of Raman intensity of SO_4~(2-)(A_s)(in 981 cm~(-1)) to(A_(B1)+A_(B2)),was also established:I_2=-0.0111+0.3653 c.However,no correlations were found between concentration of SO_4~(2-)(c) and FWHM ratios,which includes the ratio of FWHM of SO_4~(2-)(W_s) to W_(B1) W_(B2) and W_(B1+B2)(the sum of W_(B1) and W_(B2)),suggesting that FWHM is not suitable for quantitative studies of sulfate solutions with Raman spectroscopy.A comparison of Raman spectroscopic studies of mixed Na_2SO_4 and NaCI solutions with a constant SO_4~(2-) concentration and variable CI~- concentrations suggest that the I parameter is affected by CI~-,whereas the I_2 parameter was not.Therefore,even if the solution is not purely Na_2SO_4-H_2O,SO_4~(2-) concentrations can still be calculated from the Raman spectra if the H_2O band is deconvoluted into two sub-bands,making this method potentially applicable to analysis of natural fluid inclusions.
This work aims to quantify sulfate ionization concentrations in the system Na_2SO_4-H_2O using Raman micro-spectroscopy. Raman spectra of sodium sulfate solutions with known concentrations were collected at ambient temperature (293 K) and in the 500 cm_ (-4) cm ~ (-1) spectral region.The results indicate that the intensity of the SO_4 ~ (2-) band increases with increasing concentrations of sulfate ion. A linear correlation was found between the concentration of SO_4 ~ (2 -) (c) and parameter I_1, which represents the ratio of the area of the SO_4 ~ (2-) band to that of the OH stretching band of water (A_s / A_w): I_1 = -0.00102 + 0.01538 c.Furthermore, we deconvoluted the OH stretching band of water (2800 cm -1 -3800 cm -1) at 3232 and 3430 cm -1 into two sub-Gaussian bands, and then defined Raman intensity of the two sub-bands as A_ ( (3232 cm -1) and A_ (B2) (3430 cm -1), defined the full width of half maximum (FWHM) of the two sub-bands as W_ (B1) (3232 cm -1) ~ (-1)) and W_ (B2) (3430 cm -1). A linear correlat ion between the concentration of SO_4 ~ (2 -) (c) and parameter I_2, which represents the ratio of Raman intensity of SO_4 ~ (2 -) (A_s) (in 981 cm -1) to (A_ (B1 ) + A_ (B2)), was also established: I_2 = -0.0111 + 0.3653 c.However, no correlations were found between concentration of SO_4 ~ (2 -) (c) and FWHM ratios, which includes the ratio of FWHM of SO_4 (W_s) to W_ (B1) W_ (B2) and W_ (B1 + B2) (the sum of W_ (B1) and W_ (B2)), suggesting that FWHM is not suitable for quantitative studies of sulfate solutions with Raman spectroscopy. A comparison of Raman spectroscopic studies of mixed Na_2SO_4 and NaCI solutions with a constant SO_4 ~ (2-) concentration and variable CI ~ - concentrations suggest that I parameter is affected by CI ~ -, whereas the I_2 parameter was not.Therefore, even if the solution is not purely Na_2SO_4-H_2O, SO_4 ~ (2-) concentrations can still be calculated from the Raman spectra if the H_2O band is deconvoluted into two sub-bands, making this method potentially applicable to analysis of natural fluid inclusions.