Computational Modelling of the Hydride Generation Reaction in a Tubular Reactor and Atomization in a Quartz Cell Atomizer

Abstract

In this study, we present a model whereby the centre of the atomization channel is shown to be the optimal location for the spectrometric data acquisition in a quartz cell atomizer. The study aims to explore the hydride generation technique which is normally coupled with efficient thermal source to apply determination of heavy metals in water samples via spectrometric analysis. The arsenic hydride generation process and the atomization of the generated hydride in a quartz cell atomizer were studied analytically as model case studies. The hydride generation (HG) process was analyzed by adopting two hypotheses, the nascent hydrogen and formation of intermediate hydroboron species, where the results based on the second hypothesis are found to be more realistic for design purposes. Moreover, the release of the gener- ated hydride from the liquid phase and their transport to the gas phase is simulated in a helical tubular section, in which the actual tubular section length required for separation is deduced. The analytical results have been verified experi- mentally by measuring the signal intensity for the free arsenic atoms against several reaction tube lengths, in which in- creasing the tubular section length from 12 cm to 100 cm results in signal amelioration by no more than 6.6%. Further- more, the atomization of the hydride and the distribution of the generated free atoms are deduced in two configurations of tubular quartz atomizers. The results obtained from both studied cases illustrate that a high concentration of the free analyte atoms is generated in the first part of the atomization channel, saturates to a maximum in a position at the atom- izer centre, and dissipates at the inside wall of the tubular atomizer before reaching the atomizer outlet edge, which is found to be in total agreement with the current understanding of atomization mechanism in tubular atomizer and em- phasizes the fact that the centre of the quartz cell atomizer is the best location for the spectrometric data acquisition.