Ultrasound-assisted extraction of lead from solid samples: a new perspective on the slurry-based sample preparation methods for electrothermal atomic absorption spectrometry

Ultrasound-assisted extraction was attempted for the determination of Pb in slurried samples by electrothermal atomic absorption spectrometry. Slurries of a mussel tissue sample and several certified reference materials were prepared in autosampler cups for the subsequent ultrasound treatment. Three different approaches were employed with the aim of determining Pb: (i) automated ultrasonic slurry sampling; (ii) solid-liquid extraction with an ultrasonic probe; and (iii) solid-liquid extraction with an ultrasonic bath. Unlike the slurry sampling technique (i.e., the first approach), where it is mandatory to maintain a homogeneous slurry, ultrasound treatments (i.e., the second and third approaches) were focused to achieve quantitative solid-liquid extraction so that the resulting supernatant could be used for sampling. Optimum performance of solid-liquid extraction was achieved only with probe sonication. Quantitative recoveries of Pb were obtained using a 40% ultrasound amplitude, a 3 min sonication time, a 3% v/v HNO3 concentration, a particle size less than 150 mu m and a sample mass less than 20 mg slurried in a 1.5 ml acidic diluent volume. Extraction of Pb from several plant and animal tissue CRMs was also successful under the extraction conditions mentioned above. The LOD for Pb in solid biological samples using ultrasound-assisted extraction was 0.37 mu g g(-1) when 10 mg were slurried in 1.5 ml. Between-batch precision values (RSD) ranged from 1.4 to 7.3% when using ultrasound-assisted extraction with an ultrasonic probe.