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)

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.