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A novel electrochemical sensor for trace (μg/L) Uranium, based on adsorptive stripping potentiometry, is described. The sensor operation relies on the adsorptive accumulation of the uranium-cupferron complex onto a mercury-coated screen-printed carbon electrode. The disposable nature of these electrodes makes them very attractive for on-site characterization of nuclear energy sites. Various variables affecting the potentiometric stripping response were characterized and optimized to yield low-detection limit (e.g., 0.5 μg/L following a 5 minute adsorption) and good precision (relative standard deviation (RSD) = 1.4% for n = 15, 25 μg/L uranium). Convenient measurements can be carried out in nondeaerated and quiescent solutions. Applicability to the quantitation of uranium in groundwater samples is demonstrated.

Stripping analysis (SA) was successfully employed for field verification of metals contaminants in soils and sediments at hazardous waste sites. Microwave digestion procedures were tailored to meet the needs of field activities and electrochemical measurements. An adsorptive stripping voltammetric (AdSV) scheme was used for monitoring total chromium and for chromium speciation, while conventional anodic stripping voltammetry (ASV) and potentiometric stripping analysis (PSA) were used for measuring cadmium, zinc, copper, and lead. The results demonstrate that SA is capable of on-site identification of contaminated layers in soils and sediments. Concentration values measured by SA correlated well with those obtained by U.S. Environmental Protection Agency (EPA)-approved atomic or mass spectroscopy methods. The remarkable sensitivity, portability, low-power need, and low cost of SA make it an attractive choice for on-site analysis of selected metals during site characterization and remediation activities. 12 refs., 6 figs., 2 tabs.

A very sensitive stripping procedure for trace measurements of bismuth, based on the adsorptive accumulation of the bismuth-cupferron complex onto the mercury working electrode, is described. The optimized conditions include a sulfuric acid (5 × 10−4 M) medium, containing 2.5 × 10−5 M cupferron, and an accumulation potential of −0.10 V. Both voltammetric and potentiometric stripping modes can be employed to probe the reduction of the accumulated complex. The limit of detection after 10 minutes preconcentration is 6 ng L−1 (3 × 10−11 M), and the relative standard deviation at the 2 × 10−8 M level is 1.6%. Most cations, including antimony, do not interfere in the determination of bismuth. Simultaneous measurements of bismuth, titanium, and uranium are illustrated.

The adsorptive collection of the aluminum complex with cupferron is exploited for developing a highly sensitive stripping procedure for trace aluminum. Optimal experimental conditions include the use of 2 × 10−4M cupferron in PIPES buffer (pH 7.0), an accumulation potential of −0.40 V and a linear potential scan. With controlled accumulation for 2 min, a detection limit near 30 ng/l. aluminum is obtained. The relative standard deviation (at 5 μg/l.) is 2.9%. Possible interferences are evaluated. The analytical performance compares favourably with that of early adsorptive stripping schemes for aluminum.

Trace levels of uranium can be determined by stripping voltammetry after controlled adsorptive preconcentration of the uranium—cupferron complex on the mercury electrode. The resulting procedure greatly improves the selectivity over previously reported adsorptive stripping schemes, while offering similar (subnanomolar) detection limits. In addition, the use of cupferron eliminates interference from dissolved oxygen, extends the linear range, and offers a wider useful pH range. Both potentiometric and voltammetric stripping approaches are used to follow the reduction of the adsorbed complex. The effect of various experimental parameters is explored. Adaptation to flow-through cells permits on-line monitoring of trace levels of uranium at rates of 30–60 samples h −1 , with relative standard deviations of 2.7–4.1%. Applicability to the quantitation of uranium in ground water samples is demonstrated.

An automated system for on-line monitoring of trace uranium, based on a flow-through adsorptive stripping operation, is described. The on-line formation of the uranium-oxine complex is followed by its adsorptive accumulation and voltammetric quantitation at the downstream working electrode. About 10–60 runs can be made every hour with high reproducibility (RSD of 3–5%) and a detection limit of 0.7 μg/L. The dependence of the peak current on different experimental variables is reported. The sequence of events involved in the adsorptive stripping voltammetric cycle is controlled by a computer. Analogous on-line monitoring of chromium (VI) are also reported with 36 runs/h (2.1% RSD), and detection limit of 1.5 μg/L. The system holds great promise for field-based operation.

A sensitive stripping voltammetric procedure for trace measurement of thorium, based on the catalytic-adsorptive peak of the thorium—cupferron complex, is reported. Optimal experimental conditions include the use of 1mM BES buffer solution (pH 5.5), containing 20μM cupferron, an accumulation potential of −0.80 V (vs. Ag/AgCl), and a differential pulse potential scan. The resulting stripping procedure offers improved sensitivity over a previous stripping scheme for thorium. The limit of detection after 5 min preconcentration is 50 ng/l. (2 × 10−10M), the response is linear up to 8 × 10−8M, and the relative standard deviation at the 2.1 × 10−8M level is 4.4%. Possible interferences are evaluated.