Comparison of adsorptive stripping voltammetry (AdSV) and capillary zone electrophoresis (CZE) for the trace determination of selected metal ions, chelated with 2-(5′-bromo-2′-pyridylazo)-5-(diethylamino)phenol (PADAP)

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Abstract
Adsorptive stripping voltammetry (AdSV) is compared with capillary zone electrophoresis (CZE) for the detection and determination of trace concentrations of metal ions such as Co2+, Cu2+, Cd2+, Zn2+ and Pb2+ as their 2-(5′-bromo-2′-pyridylazo)-5-(diethylamino)phenol (PADAP) chelates. Limits of detection for Cd2+, Zn2+, Pb2+ and Co2+ were 9, 3, 6 and 0.3 ppb, respectively, using the AdSV method, with Cu2+ not giving a reproducible cathodic signal as the Cu2+–PADAP chelate. The technique would appear to be selective towards the determination of Co2+ in a mixture since its adsorbable chelate with PADAP was reduced at –670 mV, giving a voltammetric response not affected by the presence of equimolar concentrations (1 × 10–7 mol dm–3) of Cd2+, Pb2+ and Zn2+, CZE using PADAP at a concentration of 10–4 mol dm–3 in the run buffer had higher limits of detection than AdSV but possessed greater selectivity in that, at pH 6, Co2+, Cd2+, Zn2+ and Cu2+ could be resolved as their chelates with PADAP, the Pb2+ chelate not giving a signal at all. Other selectivities could be observed at higher pH values. The CZE technique was also found particularly responsive to the Co3+–PADAP chelate in the presence of other trace metal ions. It is therefore being investigated as a trace analytical method for the determination of Co2+ in selected complex matrices.

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