Comparison of ultrasound-assisted extraction, slurry sampling and microwave-assisted digestion for cadmium, copper and lead determination in biological and sediment samples by electrothermal atomic absorption spectrometry

Ultrasound-assisted extraction is compared with slurry sampling and microwa ve-assisted acid digestion for the determination of cadmium, lead and coppe r in biological samples and cadmium in sediment samples by electrothermal a tomic absorption spectrometry (ETAAS). The main advantage of using an ultra sound-assisted extraction in comparison to slurry sampling is a doubling of the tube lifetime for all the chosen analytes, most likely because the sam ple matrix was not introduced into the atomiser, avoiding the build up of c arbonaceous residues or silicates on the graphite platform. Consequently th e analytical variable costs were remarkably diminished. In comparison to mi crowave-assisted digestion, ultrasound-assisted extraction resulted typical ly in a two-fold better precision and better detection limits. For the extr action, slurries in nitric acid were sonicated for 2-5 min using a titanium probe. Subsequently, the solid phase was separated by centrifugation, and 20 mu l of the liquid phase was introduced into a graphite tube previously treated with a W-Rh permanent modifier. For slurry sampling, the slurries w ere sonicated for 20 s before being delivered to the W-Rh treated platform. Nitric acid concentration, sonication time, sonication power, sample mass and particle size were optimised for each analyte to obtain quantitative re coveries. For cadmium the optimum conditions (sediments and biological mate rials) were, 0.2-3.0% m/v slurry, 0.5% HNO3, 2 min sonication at 15 W. For copper and lead (biological materials only) the optimum conditions were 0.2 -2.0% m/v slurry, 5.0% HNO3, 5 min 35 W. The particle size chosen for all a nalytes was < 30 mu m. For biological materials, the extraction recoveries were: Cd, 95-105%; Cu, 90-101%; and Pb, 88-98%. However, only cadmium was q uantitatively extracted (based on the certified values of the reference mat erials) from sediment samples (recoveries 92-95%). For Pb and Cu the maximu m recoveries attained were 54% and 60% respectively. Detection limits, base d on integrated absorbance for the extracts of a 2.5% m/v biological materi al were: Cd, 3.0 ng g(-1); Cu, 88 ng g(-1); and Pb, 55 ng g(-1). For 0.5% m /v sediment the cadmium detection limit was 15 ng g(-1).