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- Title
Raman Micro-Spectroscopic Study of Sulfate Ion in the System Na<sub>2</sub>SO<sub>4</sub> - H<sub>2</sub>O.
- Authors
Dongliang, ZHU; Ziang, ZHU; Junyi, PAN; Junying, DING; Pei, NI
- Abstract
This work aims to quantify sulfate ion concentrations in the system Na2SO4-H2O 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 SO42- band increases with increasing concentrations of sulfate ion. A linear correlation was found between the concentration of SO42- (c) and parameter I1, which represents the ratio of the area of the SO42- band to that of the O-H stretching band of water ( As/ AW): I1 = -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 AB1 (3232 cm−1) and AB2 (3430 cm−1), defined the full width of half maximum ( FWHM) of the two sub-bands as WB1 (3232 cm−1) and WB2 (3430 cm−1). A linear correlation between the concentration of SO42- ( c) and parameter I2, which represents the ratio of Raman intensity of SO42- ( As) (in 981 cm−1) to ( AB1+ AB2), was also established: I2=-0.0111+0.3653 c. However, no correlations were found between concentration of SO42-( c) and FWHM ratios, which includes the ratio of FWHM of SO42- ( Ws) to WB1, WB2 and WB1+B2 ( the sum of WB1 and WB2), suggesting that FWHM is not suitable for quantitative studies of sulfate solutions with Raman spectroscopy. A comparison of Raman spectroscopic studies of mixed Na2SO4 and NaCl solutions with a constant SO42- concentration and variable Cl− concentrations suggest that the I1 parameter is affected by Cl−, whereas the I2 parameter was not Therefore, even if the solution is not purely Na2SO4-H2O, SO42- concentrations can still be calculated from the Raman spectra if the H2O band is deconvoluted into two sub-bands, making this method potentially applicable to analysis of natural fluid inclusions.
- Subjects
RAMAN spectroscopy; SODIUM sulfate; FLUID inclusions; QUANTITATIVE research; DECONVOLUTION (Mathematics)
- Publication
Acta Geologica Sinica (English Edition), 2015, Vol 89, Issue 3, p887
- ISSN
1000-9515
- Publication type
Article
- DOI
10.1111/1755-6724.12486