An automated monitor to determine trace metal particle/dissolved interactions in natural waters

Abstract

A novel automated metal monitor was optimised and validated for high temporal resolution (every 45s to 5min) measurements of dissolved Cu by adsorptive cathodic stripping voltammetry (AdCSV), Pb and Zn by anodic stripping voltammetry (ASV). The system was designed to allow the determination of both total (with UV digestion) and labile (without UV digestion) dissolved trace metal concentrations in seawater equilibrated with aerosol particles. There was negligible contamination or adsorption of trace metals from the experimental system and reaction vessel. Observed recoveries from certified reference materials for Cu, Pb and Zn were within the certified values; detection limits for total Cu, Pb and Zn were 28, 4 and 63nM, respectively.The system was applied to the investigation of the desorption of trace metals from an urban aerosol end-member (Liverpool Urban Particulate Material; LUPM, 50mgl−1) in seawater. Carefully controlled and optimised experimental conditions were implemented. The analytical limits of detection of Cu, Pb and Zn were <25% of the mean desorbed metal concentrations from LUPM. Contamination from reagents were <0.1% of the mean sample concentration. Separate experimental runs measuring the desorption of the dissolved trace metals from the aerosol sample had good repeatability (e.g. for labile determinations mean R.S.D. <5% for Zn; <10% for Cu and Pb).The high temporal resolution datasets generated by the metal monitor were used to calculate model desorption rate constants. The following range of constants were calculated 0.0047–0.015min−1 (Cu); 0.049–0.056min−1 (Zn) and 0.039–0.052min−1 (Pb).