PRECONCENTRATION OF BERYLLIUM ON THE OUTER-MEMBRANE OF ESCHERICHIA-COLI AND PSEUDOMONAS-PUTIDA PRIOR TO DETERMINATION BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

A rapid, simple and selective preconcentration method involving retention of the analyte on the outer wall of Escherichia coli and Pseudomonas putida has been developed. Several factors affecting the retention of beryllium by the outer membrane of bacterial cells were optimized. This procedure was used to preconcentrate trace amounts of beryllium prior to determination by electrothermal atomic absorption spectrometry. Both batch and immobilization techniques for the two bacteria were compared, but the former methods showed better analytical capabilities. Beryllium ions are easily retained on the outer membrane at pH 6-9 for E. coli and pH 3-10 for P. putida. The bacterial mass that retained the beryllium was centrifuged and dispersed in 3.5 mol l-1 nitric acid. The resulting slurry was introduced directly into the graphite tube. The best analytical figures of merit were obtained for E coli using a slurry sampling technique with a sensitivity and detection limit of 0.015 and 0.05 ng ml-1, respectively, for the platform atomization of beryllium in the absence of a chemical modifier. No interferences from the main major and minor ions of environmental interest were found. The proposed method was applied to the determination of beryllium in an environmental reference material.