SLURRY-ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY OF SAMPLES WITH LARGE AMOUNTS OF SILICA - DETERMINATION OF CADMIUM, ZINC AND MANGANESE USING FAST TEMPERATURE PROGRAMS

The determination of cadmium, zinc and manganese in diatomaceous earth, as well as in other materials with high silica content, is carried out by first suspending the ground samples in dilute hydrofluoric acid. Following this, aliquots of the slurries are directly injected into the electrothermal atomizer. Using the fast-temperature methodology, the drying and ashing steps,are replaced by a modified drying stage in which temperature and hold time are experimentally optimized by studying the temperature changes inside the atomizer with a thermocouple. Zinc and cadmium are atomized from a platform using ammonium phosphate as a matrix modifier. Wall atomization and no modifier other than hydrofluoric acid is used for manganese determination. Calibration is performed using aqueous standards. The optimized conditions for diatomaceous earth samples are applicable to other materials with high silica content, as is shown by the analysis of five standard reference materials.