Comparison of ultrasound-assisted extraction, microwave-assisted acid leaching and reflux for the determination of arsenic, cadmium and copper in contaminated soil samples by electrothermal atomic absorption spectrometry

Extraction methods for the determination of arsenic, cadmium, and copper in contaminated soil samples by Zeeman effect electrothermal atomic absorption spectrometry have been compared. The determination of cadmium and copper in ultrasound-assisted aqua regia extracts of contaminated soil SRMs by ETAAS, using a mixture of NH4H2PO4 and Mg(NO3)(2), for cadmium, and a mixture of Pd and Mg(NO)(2), for copper, as a matrix modifier, was carried out with high accuracy and precision (RSD < 5.1%). The analysis of SRM 2711 failed to obtain the certified concentrations of Cd and Cu by microwave and reflux methods, respectively. The determination of arsenic was performed successfully in low chloride concentrations by using a solution of 0.2% m/v NaNO3 as a matrix modifier. With chloride concentrations higher than 0.07 M the integrated absorbance signals of arsenic decreased significantly and the repeatability observed was as low as 15% for three replicate measurements. The chloride interferences on the determination of cadmium and copper were also tested with the addition of hydrochloric acid concentrations of up to 0.5 M without registering a significant decrease in the absorbance signals of the elements. The detection limits reached by the ultrasound-assisted extraction method were as low as 5, 0.04, and 0.26 mg kg(-1) for arsenic, cadmium, and copper, respectively.