Development and evaluation of diffusive gradients in thin-films technique with a novel titanium peroxide binding gel for in situ measurement of Tl in natural waters and sediments.

Speciation of thallium (Tl) controls its fate and biogeochemical behaviors. Thus, a sensitive and accurately approach for Tl monitoring is of great demand due to its ultra-low concentration and sensitivity to redox change. In this study, diffusive gradients in thin-films technique (DGT) assembled with novel titanium peroxide (TP) binding gels (TP-DGT) was developed for in situ measurement of dissolved Tl(I) and Tl(III) in waters and sediments. Laboratory test showed a linear mass accumulation of Tl(I) and Tl(III) on the TP binding gels with the deployment time from 4 to 72 h. A fascinating performance of this novel DGT was achieved in a pH range of 4-9, ionic strength range of 0.1-200 mmol L-1, and humic acid concentration of 0-30 mg L-1 with a low detection limit of 0.3 ng L-1 for Tl(I) and 0.6 ng L-1 for Tl(III). The TP binding gels own excellent stability (1-365 d) and high capacity (73.5 µg Tl disc-1) which are suitable for long-term monitoring. Field application in a river indicated that TP-DGT could work effectively, comparable to the grab sampling in waters. For the first time, the TP-DGT coupled with oxygen optode was successfully applied to map 2D distribution patterns of Tl and oxygen simultaneously in the rhizosphere of M. verticillatum L. This study confirms TP-DGT is a promising tool for routine monitoring of Tl in waters and for investigating biogeochemical processes of Tl in sediments.