Quartz tube atomizers for hydride generation atomic absorption spectrometry: mechanism for atomization of arsine. Invited lecture

Abstract

The mechanism for the atomization of arsine was studied in externally heated quartz tube atomizers of various designs. A continuous flow of arsine was generated either by reaction with sodium tetrahydroborate or by direct arsine sampling from a cylinder. The latter, together with precautions taken to ensure that inadvertent addition of oxygen to the system was minimized, made possible full control of the composition of the atmosphere in the atomizer. The effect of atomizer design, purge gas type, purge gas flow rate and atomizer temperature on the oxygen supply required for optimum sensitivity and on the curvature of the calibration graph was investigated. An extremely low supply of oxygen is required for efficient atomization of arsine in heated atomizers with narrow inlet arms. At sub-optimum oxygen supply flow rates, calibration graphs are curved significantly, and gradually approach a limiting absorbance, which depends on the flow rate of the oxygen if hydrogen is the main component in the purge gas. If there is an excess of argon over hydrogen in the purge gas, the calibration exhibits a roll-over. At least a slight stoichiometric excess of hydrogen over oxygen is essential for the atomization. The results of the experiments gave a deeper insight into the mechanism of radical formation involved in atomization of the hydride in quartz tube atomizers. The influence of various experimental parameters on the cross-sectional density of hydrogen radicals in a radical cloud, which controls atomization efficiency, was established. Possibilities for improvement of analytical performance, as a consequence of the results, are discussed.