Making ET AAS Determination Less Dependent on Vapourization Kinetics of the Analytes

Abstract

The quantification of the analytes in ET AAS is normally attained by the measurement and integration of transient absorbance. High degree of atomization and constant vapour transportation rate for the analyte atoms in the absorption volume are considered to be crucial to grant correctness of the measurements. However, the second of these conditions has, in fact, never been met in the commercial tube or tube-platform ET atomizers. The vapourization of the analyte occurs during temperature rise that affects vapour transport; vapourization temperature depends on matrix or presence of chemical modifier. In the analytical practice, the problem is normally bypassed by using reference materials with physical and chemical properties similar to those of the sample. The general solution of the problem comes from the integration of running absorbance normalized with regard to vapour transportation velocity. In this work, the approach was verified by measuring absorption signals for Ag, Cd, Mn, Pb and Tl in the tube atomizer (without a platform), monitoring the temperature of the tube and calculating the instantaneous velocity of vapour transfer and respective integration. The semi-empirical formula employed to describe vapour transport velocity included the diffusion parameters specific for each element and a common constituent, attributed to gas expansion. The measurements and numerical integration were performed using various temperature ramps for the analytes alone and those introduced together with excessive amounts of Mg and Pd. The methodology suggested reduced the error associated with change of atomization kinetics from 20 to 2 %. In combination with chemical modification the measurement methodology does not require platform atomization.

KEYWORDS ET AAS, vapour transport, chemical modification, normalization of integrated absorbance