ALUMINUM ATOM FORMATION IN ELECTROTHERMAL GRAPHITE ATOMIZER ATOMIC-ABSORPTION SPECTROMETRY STUDIED BY INSITU SPECTROSCOPIC MEASUREMENTS OF ALUMINUM AND ALUMINUM-HYDRIDE

The aim was firstly to measure quantitatively the partial pressures of Al, AlO and AlH in a graphite atomizer under analytical conditions for the determination of the Al. The absorbance spectrum of AlH was registered Photographically. With 500 ng of Al in an aqueous solution the partial pressures of Al and AlH were estimated to be of the same order of magnitude, i.e., 10 Pa, both species appearing at 2200 K. The large amount of AlH formed might explain the incomplete atomization and should, together with H-2, be considered in mechanistic descriptions of Al atom formation. Aluminium oxide could be observed in neither a spatially isothermal (integrated contact tube) nor a non-isothermal (commercially available Massmann-type) atomizer. Secondly, the aim was to investigate the effects of several analytical variables on the Al and AlH signals. This was performed in a series of experiments using fractional factorial designs. The main result was that for decreasing masses of Al, the ratio of AlH to Al decreased and the Al signal became sensitive to a new set of variables. Therefore, an atomization model based on measurements performed using microgram amounts of Al is probably not valid at the nanogram or picogram level.