| 1. |
- Corbett, Thomas, et al.
(author)
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Toward In-Field Determination of Nitrate Concentrations Via Diffusive Gradients in Thin Films-Incorporation of Reductants and Color Reagents
- 2022
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In: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 7:13, s. 10864-10876
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Journal article (peer-reviewed)abstract
- Diffusive gradients in thin films (DGTs) have been established as useful tools for the determination of nitrate, phosphate, trace metals, and organic concentrations. General use of DGTs, however, is limited by the subsequent requirement for laboratory analysis. To increase the uptake of DGT as a tool for routine monitoring by nonspecialists, not researchers alone, methods for in-field analysis are required. Incorporation of color reagents into the binding layer, or as the binding layer, could enable the easy and accurate determination of analyte concentrations in-field. Here, we sought to develop a chitosan-stabilized silver nanoparticle (AuNP) suspension liquid-binding layer which developed color on exposure to nitrite, combined with an Fe(0)-impregnated poly-2-acrylamido-2-methyl-1-propanesulfonic acid/acrylamide copolymer hydrogel [Fe(0)-p(AMPS/AMA)] for the reduction of nitrate. The AuNP-chitosan suspension was housed in a 3D designed and printed DGT base, with a volume of 2 mL, for use with the standard DGT solution probe caps. A dialysis membrane with a molecular weight cutoff of <15 kDa was used, as part of the material diffusion layer, to ensure that the AuNP-chitosan did not diffuse through to the bulk solution. This synthesized AuNP-chitosan provided quantitative nitrite concentrations (0 to 1000 mg L-1) and masses (145 mu g) in laboratory-based color development studies. An Fe(III)-impregnated poly-2-acrylamido-2-methyl-1-propanesulfonic acid/acrylamide copolymer hydrogel [Fe(III)-p(AMPS/AMA)] was developed (10% AMPS, and 90% AMA), which was treated with NaBH4 to form an Fe(0)-p(AMPS/AMA) hydrogel. The Fe(0)-p(AMPS/AMA) hydrogel quantitatively reduced nitrate to nitrite. The total nitrite mass produced was similar to 110 mu g, from nitrate. The diffusional characteristics of nitrite and nitrate through the Fe(III)-p(AMPS/AMA) and dialysis membrane were 1.40 x 10(-5) and 1.40 x 10(-5) and 5.05 x 10(-6) and 5.15 x 10(-6) cm(2) s(-1) at 25 degrees C respectively. The Fe(0)-hydrogel and AuNP-chitosan suspension operated successfully in laboratory tests individually; however, the combined AuNP-chitosan suspension and Fe(0)-hydrogel DGT did not provide quantitative nitrate concentrations. Further research is required to improve the reaction rate of the AuNP-chitosan nitrite-binding layer, to meet the requirement of rapid binding to operate as a DGT.
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| 2. |
- Mohammadi, Amir, et al.
(author)
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Application of Diffusive Gradients in Thin Films for Monitoring Groundwater Quality br
- 2022
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In: ACS - ES & T Water. - : American Chemical Society (ACS). - 2690-0637. ; 2:4, s. 518-526
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Journal article (peer-reviewed)abstract
- Diffusive gradients in thin films (DGTs) provide time-weighted solute concentrations in well-mixed fluvial environments. However, the DGT method has rarely been applied to relatively slowly moving groundwater systems, where the increased length of the diffusive boundary layer (DBL) must be accounted for, to give accurate concentration measurements. Because the DGT method pre-concentrates trace-level solutes (e.g., Cd2+) and averages out fluctuations in more dynamic contaminants (e.g., NO3-), it has potential advantages over conventional methods. This study evaluated the application of DGT methods for monitoring trace contaminants in groundwater, which are often present at levels below standard instrumental detection limits. We tested three different DGT deployment approaches using NO3- to estimate the DBL thickness: a static DGT suspension, a DGT shaker, and a pumped flow-cell unit coined the "universal DGT monitoring system" (UDMS). Unlike static and DGT shaker approaches, the UDMS reduced the DBL thickness (similar to 0.02 cm) to values within the range of well-mixed waters (DBL <= 0.03 cm). Comparable DBL thicknesses for NO3- and Cd2+ and correlations with grab sample measurements (R-2 = 0.99 and 0.98, respectively) demonstrate the suitability of DGTs combined with the UDMS for groundwater monitoring. This approach is particularly suitable for analysis of trace-level solutes including organic contaminants.
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