ELUCIDATION OF MECHANISMS THAT CONTROL THE ELECTROTHERMAL ATOMIZATIONOF TIN CHLORIDE

Mechanisms that control the electrothermal atomization of SnCl2 were i nvestigated by monitoring real-time mass spectra of gaseous species ge nerated in pyrolytic graphite coated graphite furnaces during the atom ization cycle. Vacuum and atmospheric pressure vaporization were used to help differentiate between homogeneous gas-phase and condensed-phas e interactions. During vacuum vaporization from tube atomizers, free S n was not observed and the only molecular species detected were SnO(g) and SnCl2(g). During atmospheric pressure vaporization, the observed molecular species consisted primarily of SnCl2(g) and SnO(g). Free Sn, as determined by mass spectrometry, was absent from the centre of the atomizer. Free Sn was present, however, as determined by atomic absor ption spectrometry. This suggests that atomization occurs at the regio ns of lowest temperature in the atomizer, i.e., the end regions. The t hermal decomposition of homogeneous gas-phase species cannot account f or the formation of free Sn because of the paucity of Sn(g) in the cen tre of the atomizer. However, SnO(g) interactions with the cooler surf ace regions of the graphite atomizer do explain these data. Desorption of the resulting Sn(ad) can then account for the free Sn that was obs erved as the atomizer temperature increased. This argument is supporte d by mass spectrometric results acquired when vaporizing at atmospheri c pressure from capillary-like graphite cups that were heated to exhib it temperature gradients along their lengths.