FLOW-INJECTION FLAME ATOMIC-ABSORPTION SPECTROMETRY FOR SLURRY ATOMIZATION - DETERMINATION OF IRON, CALCIUM AND MAGNESIUM IN SAMPLES WITH HIGH-SILICA CONTENT

A study on the use of slurries in flame atomic absorption spectrometry is reported. Samples with a very high silica content are ground and t hen slurried in a solution containing 2% hydrochloric and 3% v/v hydro fluoric acids. The suspensions are prepared in the 0.01-1% m/v range a nd introduced into the flame by means of a simple flow injection manif old. Relative standard deviations for the measurements of iron, calciu m and magnesium in diatomaceous earth samples are in the 1.5-2.8, 2.2- 5.3 and 2.8-5.0% ranges, respectively. To avoid the use of suspensions prepared with a very low percentage of solid sample and to improve th e reproducibility, an on-line dilution manifold is tried. The use of a n easy-to-construct variable volume dilution chamber allows the on-lin e dilution of the slurries, thus permitting the determination of calci um and magnesium over a wide range of concentrations. Calibration is p erformed using aqueous standards. The experimental conditions, optimiz ed for the determination of iron, calcium and magnesium in diatomaceou s earth samples, can also be applied to other silica-based materials, as is shown by the analysis of several standard reference materials.