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Raman Micro‐Spectroscopic Study of Sulfate Ion in the System Na 2 SO 4 – H 2 O
Author(s) -
Dongliang ZHU,
Ziang ZHU,
Junyi PAN,
Junying DING,
Pei NI
Publication year - 2015
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.12486
Subject(s) - raman spectroscopy , full width at half maximum , analytical chemistry (journal) , sulfate , ion , chemistry , sodium sulfate , spectroscopy , sodium , materials science , optics , physics , optoelectronics , organic chemistry , chromatography , quantum mechanics
This work aims to quantify sulfate ion concentrations in the system Na 2 SO 4 ‐H 2 O 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 B1 (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 2 SO 4 and NaCl solutions with a constant SO 4 2– concentration and variable Cl − concentrations suggest that the I 1 parameter is affected by Cl − , whereas the I 2 parameter was not Therefore, even if the solution is not purely Na 2 SO 4 ‐H 2 O, SO 4 2– concentrations can still be calculated from the Raman spectra if the H 2 O band is deconvoluted into two sub‐bands, making this method potentially applicable to analysis of natural fluid inclusions.