Add time:08/11/2019         Source:sciencedirect.com

The properties, sensitivity and selectivity of several catalytic adsorptive systems consisting of Co(II)-dioximate complexes (dimethylglyoxime (DMG), nioxime) and the oxidation agents (bromate or nitrite) were compared in conditions of adsorptive stripping voltammetry at the hanging mercury drop or amalgam film (Hg(Ag)FE) electrodes. For this purpose the catalytic behaviour of the catalytic systems Co(II)-nitrite and Co(II)-bromate in the absence of dioximes was also investigated. It was demonstrated that the Co(II)-(NH3)x complex induces the catalytic reduction of BrO3− ions in the ammonia buffer solution. The electrode mechanism of the reduction of the most sensitive system, i.e. Co(II)-DMG-BrO3−, was elucidated by means of cyclic voltammetry and using criteria established for square wave voltammetry. It was assumed that in the Co(II)-DMG-BrO3− system the intermediate product–the composite complex of Co(II) with DMG and BrO3− – takes part in the cyclic catalytic reduction of BrO3− ions. Combining adsorptive stripping accumulation with the catalytic enhancement of the analytical signal of Co(II)-DMG by BrO3− ensures extremely high sensitivity of Co determination.After 60 s of accumulation at −0.7 V in the supporting electrolyte containing 6.5 × 10−5 M DMG, 0.2 M BrO3− and 0.1 M ammonia buffer, cobalt may be determined in the concentration range of 5 × 10−10–1 × 10−7 M Co(II) by means of SW-CAdSV at the Hg(Ag)FE. The limit of detection was 1 × 10−10 M Co. The proposed method of cobalt determination was successfully applied and validated by studying the certified reference material TMRAIN-95 (water sample). The elaborated method ensures very sensitive determination of Co(II) as well as simultaneous estimation of Co(II) and Ni(II) in the presence of a 4000-fold excess of Zn(II).

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