Transverse heated filter atomizer: optimization of design and heating mode

Abstract

The use of a transverse heated filter atomizer (THFA) in the atomic absorption determination of volatile elements provides a substantial reduction of matrix interferences without application of chemical modifiers. The analytical effects are obtained because of a large surface, which is provided by the collector, and vapor filtration through the heated graphite. In the THFA, the heating of both the filter and collector occurs due to energy transfer from the external tube, which can be affected by characteristics of both the design and heating mode. The complicated design of the atomizer makes its analytical characteristics a priori vulnerable to random deviation of its physical characteristics or experimental conditions. Nevertheless, these negative effects can be reduced if the design and heating mode provide high and stable temperatures of the analytical zone during sample vaporization and vapor transport. The attempt to fulfill these requirements was undertaken, and the model of heat exchange between the THFA components was developed in order to improve the design and operation parameters. The final system of differential equations was solved using MATLAB software. According to theory, the reduction of filter length, increase of mass and heat capacity of the collector, provision of uniform distribution of the sample on the substrate, and low temperature of the atomizer before the vaporization step results in the required analytical properties. The theoretical recommendations were examined experimentally. The modification of the THFA according to the theoretical findings provided complete atomization for direct determination of Pb, as tetraethyl lead in organic medium, and Cd and Pb in a urine matrix. Analytical signals for Pb in both organic and inorganic matrices were found to be reproducible with RSD of 4–6% in 20 randomly selected THFA tubes. Application of the theory to the commercial transverse heated graphite atomizer with a platform (THGA) and comparison of both atomizers showed that the delayed vaporization in the THFA has a similar nature to that in the THGA in the presence of chemical modifiers.