Cloud point extraction for ultra-trace Cd determination in microwave-digested biological samples by ETAAS.

PEDRO R. ARANDA; RAÚL A. GIL; SUSANA MOYANO; IRMA DE VITO; LUIS D. MARTINEZ

TALANTA

Elsevier

Lugar: Amsterdam Holanda.; Año: 2008 vol. 77 p. 663 - 666

0039-9140

Cloud point extraction (CPE) has been used for the pre-concentration of cadmium, after the formation of a complex with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP), and further determination by graphite furnace atomic absorption spectrometry (ETAAS) using polyethyleneglicolmono-p-nonyphenylether (PONPE 7.5) as surfactant. The chemical variables that affect cloud point extraction were optimized. Separation of the two phases was easily accomplished without centrifugation, cooling the mixture in order to make more viscous the surfactant-rich phase. Also, regular Pd+Mg, Pt and permanent Ir, Rh and Ru modifiers were studied. The best thermal stabilization was obtained with Pd+Mg, with a maximum pyrolysis temperature of 1100 ºC. Under the optimum conditions i.e., pH 9.0, [5-Br-PADAP] = 2.0 ×10-5 mol L-1, [PONPE 7.5] = 0.02% w/v, an enhancement factor of 22-fold was reached. The lower limit of detection (LOD) obtained under the optimal conditions was 0.008 µg L-1. The precision for 10 replicate determinations at 0.2 µg L-1 Cd was 3.5 % relative standard deviation (R.S.D.). The calibration graph using the pre-concentration system for cadmium was linear with a correlation coefficient of 0.9984 at levels close to the detection limits up to at least 1.0 µg L-1. The method was successfully applied to the determination of cadmium in urine samples and in a water standard reference samples.