In situ redox speciation analysis of chromium in water by diffusive gradients in thin films using a DE81 anion exchange membrane

Abstract

A method for the in situ redox speciation analysis of chromium in water by the diffusive gradients in thin films (DGT) technique using a DE81 anion exchange membrane was successfully developed. For the selective uptake of Cr(VI), a DGT device containing an anion exchange membrane DE81 (cellulose acetate chromatographic paper) was used (DE81-DGT), while selective uptake of Cr(III) was carried out using DGT devices containing the Chelex-100 resin (Chelex-100-DGT). A correlation coefficient of 0.993 was obtained for the linearity of the immersion curves (mass versus time) using DE81-DGT. The diffusion coefficient values for Cr(VI) through the agarose diffusive layer were equal to 4.89±0.5×10(-6)cm(2)s(-1) and 3.95±0.02×10(-6)cm(2)s(-1) (T=23±1°C, I=0.03molL(-1) NaNO3) were obtained by using diffusion cell and immersion curves, respectively. The retention of Cr(VI) by the DE81 membrane in a synthetic sample and river water was not affected by the pH over a wide range 4-9). Recoveries of Cr(VI) between 90% and 120% from solutions of ionic strength ranging from 0.01 to 0. 5molL(-1) NaNO3 were achieved. Finally, the redox speciation analysis of Cr(III) and Cr(VI) in spiked river water and synthetic samples was performed with recoveries greater than 80% and 87% by using Chelex-100-DGT and DE81-DGT devices, respectively. Those results were in excellent agreement with the diphenylcarbazide spectrophotometric method.

Developments in the diffusive gradients in thin-films technique for the speciation of oxyanions and platinum group elements in aquatic systems

“…Since only the cationic Cr(III) species is bound (and preconcentrated) to the chelating resin, Cr(VI) would be analyzed by elution of the diffusive layer, which is depleted of Cr(III), but equilibrated with the outer sample solution for the hexavalent species (this is actually known as the Diffusive Equilibration in Thin films technique, DET [46]). This method has the obvious drawback of much higher detection limits for Cr(VI) as compared with Cr(III), which led to the subsequent development of novel DGT methods using anion exchange binding phases [47] for the selective uptake of chromate ions.…”

Diffusive gradients in thin films: devices, materials and applications

“…Li et al (2002) utilized commercially available solid cellulose phosphate membranes (Whatman P81) as DGT binding phase to determine Cu and Cd, and this type of DGT has been extended to measurement of other metals, such as Cd, Cu, Pb, Zn, Co, Ni, Mn, Ba, Hg and U species (Colaço et al 2014;de Oliveira et al 2012;Larner and Seen 2005;Mengistu et al 2012;Pedrobom et al 2017). In addition, the Whatman DE 81 with amino functional groups has been applied for the measurement of U species and Cr(VI) in waters (Li et al 2006;Pedrobom et al 2017;Suárez et al 2016).…”