Ultrasound-assisted extraction of cadmium from slurried biological samples for electrothermal atomic absorption spectrometry

Cadmium was determined in biological materials by electrothermal atomic absorption spectrometry after ultrasound-assisted treatment of slurried samples prepared in the autosampler cups with an acidic diluent. Parameters influencing Cd extraction into the liquid phase of the slurry, such as ultrasound amplitude, sonication time, particle size, acid concentration and sample mass used for preparing the slurry, were investigated. Quantitative recoveries of Cd from mussel tissue were obtained using a 20% amplitude, a 1 min sonication time and 3% nitric acid, demonstrating that the resulting supernatant in the autosampler cup can be used for sampling. Particle size had no effect on Cd extraction from mussel tissue in the range <50 and >200 &mu;m, the recovery being quantitative. Extraction of Cd from several CRMs, such as BCR CRM 60 (Lagarosiphon major) Aquatic Plant, BCR CRM 278 Mussel Tissue, NRCC DORM-2 Dogfish Muscle and NRCC DOLT-2 Dogfish Liver, was also successful under the conditions mentioned above along with the original particle size distribution provided for these materials. Non-quantitative extraction was obtained with materials that have a typical inorganic matrix, such as BCR CRM 145R Sewage Sludge and BCR CRM 320 River Sediment. Homogeneity testing was carried out by comparison of between- and within-batch precision as well as homogeneity factors. The LOD for Cd in the solid biological samples was 0.019 &mu;g g –1 when a 10 mg sample mass was slurried in a volume of 1.5 ml. In all cases, an acceptable homogeneity was observed even when using a sample mass of 10 mg for slurry preparation. In addition, the proposed approach for analyte extraction should provide further advantages in comparison with conventional slurry sampling, such as an improved precision, since the representative sub-sample is the whole mass taken for slurry preparation, lower background signals and a decreased build-up of carbonaceous residues inside the graphite tube.