Improving elution strategies for Chelex®-DGT passive samplers

Abstract

Elution of Chelex® binding layers, commonly used for the diffusive gradients in thin films technique (DGT), is recognized as the most important contributor to the uncertainty of DGT measurements. Limiting uncertainty requires the use of optimized procedures and suitable elution recoveries (f _e ). This work therefore investigated elution robustness to propose improved strategies. A wide range of conditions were investigated for the main elution parameters (Chelex® particle size, elution time, Chelex® loading, and eluent concentration and volume) on Al(III), Cd(II), Co(II), Cr(III), Cu(II), Ni(II), Pb(II), and Zn(II). Results showed that the choice of elution conditions should be a compromise driven by study constrains in terms of accuracy, repeatability, sensitivity, and targeted elements. Using experimentally determined recoveries should improve accuracy by approximately 5 to 10% compared to the use of recoveries from the literature. Fast elution of 1 h can be achieved without significant loss of recovery and repeatability except for Cr(III) (8 h minimum). Elution recovery depended on Chelex® loading for Zn and Cr and introducing recoveries adapted to the loading could improve accuracy up to, respectively, 11 and 27%. When standard recoveries are used, a 0.85 f _e value would be more appropriate than the common value of 0.8 to minimize inaccuracy (except for Cr). Some flexibility can be applied to elution conditions without a significant change in recovery for most elements: HNO₃ concentration of 1–15 M, volume of 1–2 mL, duration of 8–48 h. Cr(III) was unique in its sensitivity to elution condition variations; thus, choice is more restricted for this element.

Graphical abstract