Transverse heated filter atomizer: the first approximation to the model of vapor transport

Abstract

The transverse heated filter atomizer (THFA) provides substantial advantages in trace element determination, due to the efficient suppression of interferences. This advancement is determined by the THFA design and the properties of its components: the pyrocoated graphite tube, the sample collector (carbon fiber and refractory wire) and the graphite filter.

The sample vapor transport and the formation of an analytical signal in the THFA are discussed in this work as a continuation of already published research concerning heat transfer in the atomizer. The system of first order differential equations of mass- and heat transfer is solved numerically using the Matlab software. The concept enables one to simulate atomic absorption peak depending on the physical parameters of the atomizer, the temperature program and the assumptions regarding the vaporization, atomization and vapor filtration. As the first approach in this work those processes are considered not affected by interaction with the substrate and filter material.

The experimental verification of the theory was performed by comparing the atomization pulses of Pb and Cd in the transverse heated graphite atomizer (THGA) and THFA. The theory is satisfactory as far as the atomic absorption peak area is concerned, which enables optimization of filter configuration and evaluation of vapor losses through the sampling hole. The optimal length of the filter providing efficient atomization and minimum vapor losses is about one third of the THFA tube, that is, 0.6–0.7 cm. The sensitivity ratio between the THFA and THGA is equal to 2.2–2.3 in favor of the THFA. The plugging of the THFA sampling hole can further increase the ratio to 3.3–3.7 times.

The atomic absorption signals in the experiment are shifted towards later times to a greater extent than predicted by the theory. This indicates the presence of concomitant processes of vapor absorption–desorption on the substrate and interaction of the analyte with graphite. Apparently, those processes should be taken into account in undertaking further development of the theory.