Renewable-reagent electrochemical sensor for monitoring trace metal contaminants

This work extends the concept of in situ electrochemical stripping sensors to environmentally important metals that are not readily accumulated by amalgamation. A renewable-reagent sensor has thus been designed to accommodate the complex formation and adsorptive accumulation steps of adsorptive stripping protocols. Such flow probe relies on the delivery of a ligand solution through a microdialysis sampling tube and transport of the resulting complex to a downstream adsorptive stripping detector. The integrated membrane sampling/adsorptive stripping sensor is characterized, optimized, and tested in connection with the monitoring of trace uranium and nickel using the propyl gallate and dimethylglyoxime chelating agents, respectively. Experimental variables, including the reagent delivery rate and ligand concentration, are explored. The microdialysis sampling step minimizes the interference of surface-active macromolecules and extends the linear dynamic range compared to conventional adsorptive stripping measurements. Detection limits of 1.5 x 10(-8) M nickel and 4.2 x 10(-8) M uranium are obtained following 5- and 20-min adsorption times. A relative standard deviation of 1.7% is obtained for prolonged operations of 20 runs. The applicability to assays of river water and groundwater samples is demonstrated. The renewable-reagent adsorptive stripping sensor holds great promise for remote monitoring of various trace metals (via a judicious selection of the ligand).