APPLICATION OF THE KELVIN EQUATION TO VAPORIZATION OF SILVER AND GOLDIN ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

In order to obtain additional insight into the release mechanism of th e metals in electrothermal atomization atomic absorption spectrometry, a quantitative relation between the heat of vaporization and the size of the released particles is proposed on the basis of the Kelvin equa tion, The applicability of the equation for the investigation of silve r and gold vaporization is demonstrated and the limits in which the mo del is valid are determined. According to the present considerations t he activation energy could be equal to the heat of vaporization of the silver and gold droplets. An explanation of the observed dependence o f activation energy on analyte mass is given. The proposed relation pr ovides a possibility for definition and evaluation of an ''effective'' radius/size of the droplets on the basis of their heat of vaporizatio n. A correlation between the mass of the injected sample and the ''eff ective'' radius of the droplets, obtained at higher temperature is fou nd. The minimum and maximum ''effective'' radii of the droplets, follo wing the proposed equation are calculated for Ag On pyrolytic graphite coated electrographite (PGC) and Au on PGC, uncoated electrographite (EG) and glassy carbon (GC) tubes. The results obtained are indirect e vidence for the island structure of precursor metal layer and for the existence of silver and gold microdroplets on the graphite support.