Supercritical fluid extraction of cadmium as Cd–oxine complex from human hair, Determination by square wave anodic or adsorptive stripping voltammetry

A method is presented for the extraction of cadmium as the Cd(Ox)2 complex with methanol-modified supercritical CO2. In a first step, aliquots of Cd2+ solutions were spiked onto filter paper and air-dried, and the filter paper with cadmium, oxine and methanol was placed in a 10 ml stainless steel extraction vessel. A study was made of extraction as a function of pressure (6.9–24.1 MPa), oven temperature (40–200 °C), restrictor temperature (20–100 °C), presence of modifier (1.0–4.0 ml), and static extraction time (10–50 min). Quantitative extractions of cadmium were achieved when the experiments were carried out at 17.2 MPa, 80–120 °C oven temperature, 60 °C restrictor temperature, 2.0–3.0 ml of methanol, 30 min static extraction, and 5 min in dynamic mode. An aliquot of the extract was placed in an electroanalytical cell that contained a supporting electrolyte, and cadmium was quantified by square wave stripping voltammetry. The calibration graphs using cadmium solutions in the presence of 0.1 M of oxine were linear over a 5.0–120.0 (mu)g l^-1 range. The detection limits using anodic stripping voltammetry or adsorptive stripping voltammetry were 1.5 and 1.4 (mu)g l^-1 of cadmium, respectively. The efficiency of the extraction was evaluated using certified reference human hair. The procedure was then applied to cigarette samples and to hair of cigarette smokers and non-smokers. Cadmium concentration ranges were 0.06–0.57 (mu)g g^-1 (average 0.25(plus-minus)0.18 (mu)g g^-1) for smokers and 0.02–0.26 (mu)g g^-1 (average 0.11(plus-minus)0.07 (mu)g g^-1) for non-smokers.