Quartz tube atomizers for hydride generation atomic absorption spectrometry: mechanism of selenium hydride atomization and fate of free atoms

Abstract The influence of the purge gas type and its flow, as well as the oxygen supply and the temperature on the selenium sensitivity of a commercial, externally heated quartz tube atomizer, was investigated. The gas flow acts analogously as in the flame-in-tube atomizers, and the type of gas influences the atomic absorption coefficient. There is a synergic effect of oxygen supply and temperature on the sensitivity in a broad temperature range starting below 600°C. The higher the temperature, the lower oxygen supply required to achieve optimum sensitivity. A “hybrid” hydride atomizer, capable of working as either a flame-in-tube atomizer or an externally heated quartz tube atomizer, or in several combined modes, was employed to investigate hydride atomization and analyte transfer in quartz tube atomizers. The following conclusions have been drawn from the experiments: (i) There is no fundamental difference between both types of quartz tube atomizers, externally heated quartz atomizers being, in fact, oxygen-deficient, externally heated flame-in-tube atomizers. Hydride atomization takes place in a small cloud of hydrogen radicals located at the entrance to the heated portion of the cell. The decay of analyte free atoms takes place on the whole inner atomizer surface; (ii) The decay rate increases with temperature. This increase is much more pronounced if the surface is contaminated. The contamination does not affect the efficiency of atomization in the radical cloud; (iii) Typically, the sensitivity is controlled by the rate of free atom decay; and (iv) Decayed Se species are volatile-they can be completely reatomized in an additional flame downstream in the atomizer either externally heated or unheated. They cannot be atomized at all in a heated atomizer without a separate oxygen inlet.