A physical approach to the interpretation of the mechanisms and kinetics of analyte release in electrothermal atomic absorption spectrometry

The first part of this review is devoted to a substantiation of the physical approach to the interpretation of the exponential dependence of the rate of heterogeneous reactions on temperature proposed by Hertz and Langmuir, and developed by the author as an alternative to the traditional chemical approach based on the Arrhenius concept of the activation effect. The second part of this work is devoted to the application of this approach to the identification of the mechanisms of analyte release in electrothermal atomic absorption spectrometry. The most important results of this application, which support advantages of the physical approach over the traditional chemical approach, are the following: a method of theoretical calculation of the absolute rates for solid-state decomposition reactions has been developed; some unusual peculiarities in kinetics of analyte atomization (double values of the E-parameter and high values of the pre-exponential factor in the Arrhenius equation) were interpreted; the mechanism of low-temperature migration of analyte in graphite tubes at pyrolysis temperatures and, in particular, analyte migration onto a palladium modifier was explained; and two simple criteria have been proposed for the identification of the true mechanism of analyte release as either bulk evaporation/desorption alternative and on this basis the mechanism of analyte retention on a Pd modifier has been interpreted. It has been concluded that the application of the chemical approach, based on the Arrhenius concept of the activation effect to the kinetics of heterogeneous reactions, was wrong, and has resulted in a stagnation of theory over many years.