Simultaneous Measurement of Trace Metal and Oxyanion Concentrations in Water using Diffusive Gradients in Thin Films with a Chelex–Metsorb Mixed Binding Layer

Abstract

A new diffusive gradients in thin films (DGT) technique with a mixed binding layer (Chelex-100 and the titanium dioxide based adsorbent Metsorb) is described for the simultaneous measurement of labile trace metal (Mn, Co, Ni, Cu, Cd, and Pb) and oxyanion (V, As, Mo, Sb, W, and P) concentrations in freshwater and seawater. The mixed binding layer (MBL) DGT technique was evaluated against the Chelex-DGT and Metsorb-DGT techniques, and all elution efficiencies and diffusion coefficients have been remeasured for the above analytes. Diffusion coefficients (D) measured using MBL-DGT generally agreed well with those measured by Chelex-DGT (DMBL/DChelex = 0.97-1.05), Metsorb-DGT (DMBL/DMetsorb = 0.97-1.01), and diffusion cell experiments. The measurement of trace metals and oxyanions by MBL-DGT was independent of pH (5.03-8.05) and ionic strength (I = 0.001-0.7 mol L(-1)). MBL-DGT accurately measured the concentration of trace metals and oxyanions in synthetic freshwater (CMBL/CSol = 0.82-1.18) over the 4 day deployment and also agreed well with Metsorb-DGT (CMBL/CMetsorb = 0.84-0.94) and Chelex-DGT (CMBL/CChelex = 0.88-1.11) measurements. In synthetic seawater, MBL-DGT accurately measured the concentration of metals and oxyanions (CMBL/CSol = 0.85-1.12) over 4 days, with the exception of Mo-none of the DGT techniques were capable of measuring Mo in seawater. MBL-DGT measured the Mn concentration accurately over the entire 4 day period, whereas Chelex-DGT only measured Mn accurately up to 2 days. The MBL-DGT method described in this study offers significant advantages over the ferrihydrite-Chelex-DGT method reported previously. These advantages include the commercial availability of both Metsorb and Chelex-100, the higher accuracy of Metsorb for measuring some oxyanions in freshwater and seawater, and the possibility of measuring Fe, which would not be possible using the Chelex-ferrihydrite binding layer.

High-resolution measurement and mapping of tungstate in waters, soils and sediments using the low-disturbance DGT sampling technique

“…This is further supported by the Dcell value (6.60×10 -6 cm 2 s -1 ) with the matrix being changed to authentic freshwater, which agreed quite well with the synthetic NaNO3 solutions, demonstrating the good applicability of laboratory-measured Dcell value in field waters. The DDGT value (6.31×10 -6 cm 2 s -1 ) of W in this study was close to those published by Panther et al [24,28] and Shiva et al [49] (6.26/6.88/6.05/6.50×10 -6 cm 2 s -1 ) but 12% higher than the value (5.56×10 -6 cm 2 s -1 ) reported by Österlund et al [29]. In this study, an average Dcell value of 6.63×10 -6 cm 2 s -1 with IS varied from 0.001 to 0.5 mol L -1 was used for the calculation of DGT-measured concentrations.…”

“…The D values of W at 25 o C are listed in Table 1 Panther et al [24,28], but higher than the value (5.45×10 -6 cm 2 s -1 ) proposed by Österlund et al, [29].. However, when the IS was changed to a very low level of IS at 0.1 mmol L -1 , which is rare, the measured Dcell value increased by 40% to 9.26×10 -6 cm 2 s -1 .…”

“…Well-washed diffusive gels have a very small positive charge, so that in waters with such low IS (0.1 mmol L -1 ), Donnan partitioning at the gelsolution interface could occur [48], causing the effective D values of the anionic species to be elevated [33]. But such effect is negligible when IS at 0.001-0.5 mol L -1 , considering that the rather small error (2%) is comparable to those (1%-5%) measured at the same condition (IS=0.01 mol L -1 ) [24,28,29,49]. This is further supported by the Dcell value (6.60×10 -6 cm 2 s -1 ) with the matrix being changed to authentic freshwater, which agreed quite well with the synthetic NaNO3 solutions, demonstrating the good applicability of laboratory-measured Dcell value in field waters.…”

“…Analytes diffuse through the filter membrane and diffusive layer from water or porewater and are immobilized onto the binding layer. DGT containing Metsorb (titanium dioxide) or mixed Chelex-Metsorb binding layers (slurry gels) have been used to measure various dissolved oxyanions including W [24,28]. DGT loaded with a slurry ferrihydrite (SF, iron oxide) binding layer has also been reported to be able to measure W [29], but the sampler's performance responses to changing ionic strength, pH and solution W concentrations are still not known.…”

Dynamics of phosphorus–iron–sulfur at the sediment–water interface influenced by algae blooms decomposition

“…It can minimize the problems associated with conventional sampling methods such as analyte contamination and analyte speciation change during the sampling process [25,26]. This technique has unique advantages in allowing in situ measurements of a number of solutes at a high spatial resolution, which enables it to be a powerful tool in interpretation of biogeochemical processes related to key elements [16,24,27,28]. Recently, Motellca Hein et al [29] and Robertson et al [30,31] successfully applied a combined DGT to simultaneous measurements of Fe and S at a millimeter resolution [29][30][31].…”