On-line atomization of selenium hydride in graphite furnaces: mechanism and interferences

Abstract

Pure selenium hydride sampled from a gas sampling system was atomized in the transversely heated graphite atomizer in the temperature range between 600 °C and 2500 °C. Argon and hydrogen were used as the atomization atmosphere in the presence of varied amounts of oxygen. Also atomization interferences due to arsine, generated by the conventional reaction with tetrahydroborate in a continuous flow arrangement, were determined. The extent of arsine atomization was estimated also. All data were compared with equilibrium thermodynamic calculations. Below 1100 °C, the system in the atomizer is far from equilibrium; the mechanism of hydride atomization is due to collisions with hydrogen radicals formed in the furnace by reactions of oxygen with hydrogen, and analyte free atoms are removed from the observation volume mainly by chemical reactions. At temperatures above 1000 °C, the thermal mechanism of hydride atomization starts to be effective. When the formation of hydrogen radicals is prevented signals appear at temperatures above 1100 °C and the system in the atomizer is close to thermodynamic equilibrium. However, in the presence of high concentrations of As, atomization interferences were observed even at 1800 °C, which is not compatible with thermodynamic equilibrium.