Better understanding and applications of ammonium 12-molybdophosphate-based diffusive gradient in thin film techniques for measuring Cs in waters

摘要

This study deals with further and systematic laboratory evaluation of the already known ammonium 12-molybdophosphate (AMP)-diffusive gradient in thin film (DGT) method, which is used for measuring total Cs concentration in environmental waters. This study confirms that the AMP-binding gel is not stable for pH6. In order to reveal a potential impact of AMP degradation on DGT application, time-series experiments were performed by deploying AMP-DGT samplers in Cs-doped moderately basic soft and hard water up to total AMP-binding gel degradation (60 and 175h of deployment time, respectively). Linear accumulation of Cs by AMP-DGT samplers was observed up to 48 and 58h in hard and soft waters, respectively. For this deployment time range, AMP-DGT measured over 7710 and 9416% of total Cs concentration in hard and soft water, respectively. The difference in DGT response was attributed to Ca2+ and Mg2+ competition reducing the uptake of AMP-DGT samplers in hard water. Shrinkage of agarose-polyacrylamide diffusive gel was experimentally observed only in hard water due to more intensive AMP-binding gel degradation in hard water. Even if the AMP-DGT response was not impacted in this study, it is recommended to use agarose hydrogel as standard diffusive gel. Based on the experience obtained from this detailed validation process, the authors propose a number of key requirements that need to be considered when developing DGT devices, with testing the performance over longer deployment times being critical.