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Determination of cobalt(II) at a 5-[(4-chloro phenyl) azo-N-(4'-methyl phenyl)]salicyl aldiminemodified carbon paste electrode by differential pulse cathodic voltammetry
Mohammad Reza Nateghi, Ali Hadji-Shabani, Majid Fakheri
The feasibility of a carbon paste electrode(CPE) for practical use in analysis of cobalt(II) was investigated. The procedure involves an accumulation of cobalt on a 5-[(4-chloro phenyl) azo-N-(4'-methyl phenyl)]salicyl aldiminemodifiedCPE, followed bymediumexchange to a ‘clean’ solution where the accumulated Co(II) was oxidized and then a stripping voltammetric reduction current of cobalt(III) wasmeasured at the 150mV versusAg/ACl. The optimumconditions for determination of cobalt were found to be 0.09mol/l, NH3(pH=10.60) as accumulationmedium, 180s accumulation time in open circuit condition and stirred sample solution, 0.1mol/lKOH asmeasurementmedium, and 3%ligand in the composition of electrode. The relative standard deviations for 5 successive determinationswere 5.55%and 7.05%for 1.0010-5mol/l and 1.0010-6mol/l cobalt(II) respectively. The detection limit was estimated to be 8.9010-8mol/l(5.25 ppb). Excess amounts of Cu(II) interfering with cobalt peak were precipitated by potassium hexacyanoferrate(II) in acidic solution. The developed method was tested by analyzing a reference sample(Canadian certified referencematerialsNICKEL-COPPER-COBALTORESU-1a) and then applied to determineCo(II) in naturalwater andwelding electrode samples tion was found to be 20 and 4ng/ml for CT andAM respectively.
