Slurry preparation by high-pressure homogenization for the determination of heavy metals in zoological and botanical certified reference materials and animal feeds by electrothermal atomic absorption spectrometry

Abstract

High-pressure homogenization was evaluated for the preparation of slurries suitable for the determination by ETAAS of Cr, Cu, Fe, Mn, Ni and Se in soft organ tissues (liver and kidney), certified reference materials of biological and botanical origin and animal feeds. Frozen fresh organ tissue, (2 g) or certified reference material or dried, ground plant material (0.1 g) was blended, at high speed with 20 ml of ethanol-water (1 + 9 v/v) containing 0.25% m/m of tetramethylammonium hydroxide and the resulting mixture was subjected to homogenization at 38.9 MPa. After four passes through the homogenizer, the resulting solution was suitable for analysis by ETAAS. Capping the flat valve head of the homogenizer with a ruby disc appreciably reduced (but did not eliminate) metal contamination introduced by the processing. Homogenization of botanical reference materials or dried animal feeds resulted in preparations with variable amounts of residual fibres and particulate matter in the resulting suspensions. Nonetheless, all the Cu and Mn and virtually all of the Fe had been transferred to the supernatant fraction and remained with that fraction for at least 10 d. The addition of EDTA to the solvent modestly increased the mobilization of Fe from the matrix but also increased the contamination from the homogenizer. The slopes of the calibration curves generated by the method of standard additions were not significantly different from those of calibration curves generated with aqueous standards in a homogenized blank indicating that there was no significant matrix effect for any of the analytes in the nine reference materials, liver or kidney or the five animal feed samples and that aqueous standards could be used to calibrate the instrumental response.