INVESTIGATION OF REACTIONS AND ATOMIZATION OF ARSINE IN A HEATED QUARTZ TUBE USING ATOMIC-ABSORPTION AND MASS-SPECTROMETRY

Experiments were carried out to investigate reaction mechanisms of arsine and the atomization of arsenic in a heated quartz tube atomizer using atomic absorption and mass spectrometry detector systems. Arsine was generated in a reaction with sodium tetrahydroborate and collected in a cold trap. After revolatilization, the arsine was transported into the heated quartz tube with a flow of pure gas. Hydrogen, deuterium, helium and nitrogen, respectively, were used as transport gases. Evidence for the equilibrium reaction AsH3 + H ⇌ AsH2 + H2 was found at temperatures around 600°C and for the back-reaction 2 As + 3 H2 → 2 AsH3 at 900°C. In the absence of hydrogen, arsine is thermally decomposed but not atomized; elemental arsenic is retained quantitatively in the heated quartz tube under these conditions. In the presence of hydrogen, arsenic atoms form at temperatures above 650°C by reacting with hydrogen radicals. Arsenic atom attrition occurs by formation of molecular arsenic (As2 etc) and/or arsenic clusters. These forms of arsenic are retained in the heated quartz tube only to a small extent and can be transported over relatively long distances. At about 900°C free arsenic atoms react with hydrogen to form arsine. Hydrogen also reacts with deposited arsenic to form arsine at this temperature. Arsenic species containing oxygen were not detected in any of the experiments. © 1990.