Analysis of seawater for dissolved cadmium, copper and lead: an intercomparison of voltammetric and atomic absorption methods

A highly sensitive voltametric technique was developed for the direct determination of cobalt and nickel in seawater at picomolar and nanomolar concentrations, respectively. Cyclohexane-1,2-dione dioxime (nioxime) complexes of Co(II) and Ni(II) were concentrated from 10 mL of sample onto a hanging mercury drop electrode by controlled adsorption and the current resulting from reduction of Co(II) and Ni(II) was measured by differential pulse cathodic stripping voltametry. Detailed experiments were conducted to determine the optimal ligand type and concentration, buffer type and concentration, pH, and adsorption potential. Maximum sensitivity was obtained by using a nioxime concentration of 1 x 10/sup -4/ m, a HEPES buffer concentration of 0.03 m, a solution pH of 7.6, and an adsorption potential of -0.6 V. Replicate analyses of seawater reference materials yielded excellent agreement with certified values. Analytical precision for Co and Ni at coastal and open ocean concentrations was approximately +/-5% relative standard deviation. Detection limits for Co and Ni depend upon reagent blanks and are 6 pM and 0.45 nM, respectively, for 15-min adsorption periods.

Direct determination of dissolved cobalt and nickel in seawater by differential pulse cathodic stripping voltammetry preceded by adsorptive collection of cyclohexane-1,2-dione dioxime complexes

General and specific contamination factors affecting accuracy of results in heavy metal analysis at the trace level, with particular reference to the determination of Zn, Cd, Pb, Bi and Cu, are evaluated. Precautions are described to achieve a contamination controlled laboratory in general and manipulation places in particular. Pretreatment and cleaning procedures for sampling bottles and other labware, contamination-free filtration of samples and their long-term storage are dealt with. The recommended procedures ensure a satisfactory elimination of contamination and emphasize the significance of the described preparatory steps and precautions during sample handling, to achieve accurate and consequently relevant analytical results, points which have been frequently underestimated in the past.

Prevention of contamination and other accuracy risks in voltammetric trace metal analysis of natural waters

Self-assembled monolayers of ω-mercaptocarboxylic acids, HS(CH 2 ) n H (n=1, 2, 5, 10), on mercury film (MF) and gold electrodes have been used for the very sensitive and selective analysis of ultralow levels of cadmium(II). We find that shorter ω-mercaptocarboxylic acids provide superior sensitivity. Other parameters that govern the sensitivity and selectivity of this system have been examined in detail. Optimizing these factors resulted in a detection limit of 4×10 -12 M (0.45 ppt)

Self-assembled monolayers in electroanalytical chemistry: Application of .omega.-mercaptocarboxylic acid monolayers for electrochemical determination of ultralow levels of cadmium(II)

Prevention of contamination and other accuracy risks in voltammetric trace metal analysis of natural waters@@@Vermeidung von Kontamination und anderen die Richtigkeit beeinflussenden Einwirkungen bei der voltammetrischen Spurenanalyse in natrlichen Gewssern: Part III. Voltammetric ultratrace analysis with a multicell system designed for clean bench working@@@Teil III. Voltammetrische Ultraspurenanalyse mit einem Multizellensystem zum Einsatz unter einer clean bench

P. Valenta

Papers

New potentialities in ultra trace analysis with differential pulse anodic stripping voltammetry