1-(2-Pyridylazo)-2-naphthol modified carbon paste electrode for trace cobalt(II) determination by differential pulse cathodic voltammetry

Abstract

A differential pulse cathodic voltammetric method was developed for the sensitive and selective determination of Co(II) at a l-(2-pyridylazo)-2-naphthol modified carbon paste electrode. The analysis procedure consisted of an open circuit accumulation step in stirred sample solution. This was followed by medium exchange to a 'clean' solution where the accumulated Co(II) was oxidized and subsequently a cathodic potential scan was effected to obtain the voltammetric peak. The precisions obtained for 10 successive determinations each of 1.00 x 10-6 mol l-1, 1.00 x 10-7 mol l-1 and 1.00 x 10-8 mol l-1 Co(II) were 2.80, 5.14 and 9.67% (relative standard deviations), respectively. The detection limit was estimated to be 5.9 x 10-9 (0.35 ppb) (S/N = 3), for 180 s accumulation. Of the 35 selected substances examined for interferences, only V(II), Ce(III), EDTA and Triton X-100 interfered. These interferences could be easily eliminated. The developed method was tested using a certified sample (USEPA WP 386) and then applied to the determination of Co(II) in human hair, pig liver and spinach samples.