Development of on-line electrochemical sample pretreatment methods for the analysis of thallium and uranium by ICP-MS

Anodic and adsorptive stripping voltammetry (ASV and AdSV, respectively) were performed on-line with a mercury thin-film electrode (MTFE) to effect the selective accumulation and detection of thallium and uranium, respectively. ASV-ICP-MS experiments using thallium as the test element were performed to characterize the behavior of the on-line system for low level and quantitative determinations. Excellent linearity in response was demonstrated for thallium standards ranging from 0.25 ng/L to 50 μg/L. The 1.0 pg/L detection limit calculated from this data for thallium (3 σ/sensitivity) was 400 times lower than that of our conventional ICP-MS. The ability to overcome sample matrix effects in quantitative determinations was demonstrated by the analysis of an undiluted synthetic urine sample. AdSV-ICP-MS experiments were performed using uranium as the test element to demonstrate the utility of this method for the determination of radiologically important elements. A uranium(VI)-cupferron complex was used to effect adsorptive accumulation of uranium from a 10 μg/L standard solution onto the MTFE. The uranium was 'chemically stripped' from the electrode for subsequent downstream detection by the ICP-MS. The quantitative nature of this method and a modest enhancement of signal levels (approx. × 10) over those levels obtained with our conventional ICP-MS for samples in the microgram/litre concentration range were demonstrated. Modifications to the current system to provide low flow rate operation will allow further optimization of the ASV-ICP-MS and AdSV-ICP-MS combinations.