Selective Monitoring of Oxyanion Mixtures by a Flow System with Raman Detection

Abstract

Raman spectroscopy is a selective detection system scarcely applied for the flow analysis of solutions with the aim of detecting several compounds at once without a previous separation step. This work explores the potential of a portable Raman system in a flow system for the selective detection of a mixture of seven oxyanions (carbonate, sulphate, nitrate, phosphate, chlorate, perchlorate, and thiosulphate). The specific bands of these compounds (symmetric stretching Raman active vibrations of carbonate at 1068 cm−1, nitrate at 1049 cm−1, thiosulphate at 998 cm−1, phosphate at 989 cm−1, sulphate at 982 cm−1, perchlorate at 935 cm−1, and chlorate at 932 cm−1) enabled their simultaneous detection in mixtures. Although the oxyanions’ limit of detection (LOD) was rather poor (in the millimolar range), this extremely simple system is very useful for the single-measurement detection of most of the oxyanions in mixtures, without requiring a previous separation step. In addition, quantitative determination of the desired oxyanion can be performed by means of the corresponding calibration line. These are important advantages for controlling in-line processes in industries like those manufacturing fertilizers, pharmaceuticals, chemicals, or food, among others.

High Na‐ion conductivity and mechanical integrity of anion‐exchanged polymeric hydrogel electrolytes for flexible sodium ion hybrid energy storage

“…Raman spectra in Figure 2C show a strong peak at 933.06 cm −1 for the samples immersed in aqueous ClO 4 − containing solutions of LiClO 4 , NaClO 4, and Al(ClO 4 ) 3 . Moreover, the peak of ClO 4 − at 933.06 cm −1 confirms that a reaction took place between x‐polyDDA and ClO 4 − , 33,34 as described in Figure 2B. This ClO 4 − peak of the x‐polyDDA hydrogel films shows a marginal variation with reference to that of the ClO 4 − in the aqueous solution.…”

“…Therefore, the degree of polymerization of x-polyDDA becomes higher than that of commercial polyDDA (M w 200 000-550 000). FT-IR and Raman spectroscopies were applied to further investigate the anion exchange reaction of the x-polyDDA as shown in Figure 2B confirms that a reaction took place between x-polyDDA and ClO 4 − , 33,34 as described in Figure 2B. This ClO 4 − peak of the x-polyDDA hydrogel films shows a marginal variation with reference to that of the ClO 4 − in the aqueous solution.…”