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A highly selective method for the determination of cobalt with a chemically modified carbon paste electrode Is proposed. It Is based on the chemical reactivity of an Immobilized modifier, 2,2-bipyrldyl, toward cobaH(II) Ion to yield the corresponding cation complex ((Bpy)3Co)2+, which Is taken up by another modifier, perfluorinated sulfonated polymer (Nation). Differential pulse voltammetry Is employed, and the oxidation of the complex, at +0.1 V vs SCE, Is observed. For a 5-mln preconcentration period, a linear calibration curve Is obtained for cobalt concentrations ranging from 7 X 10"7 to 1 X 10~5 mol/L, and the detection limit Is 3 X 10'7 mol/L. A lower detection limit can be obtained for longer preconcentration times. For eight preconcentratlon/determlnation/renewal cycles, the differential pulse voltammetric response could be reproduced with 4.3% relative standard deviation. Rapid and convenient acid renewal allows the use of an individual modified electrode surface In multiple analytical quantitations.Many coexisting metal Ions have little or no effect on the determination of cobalt. The procedure was applied to the determination of cobalt for four standard reference materials with relative standard deviation of 4.0-5.2%.

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