Some observations on sulfuric acid reactions in electrothermal atomic absorption spectroscopy with graphite furnaces

Interferences were found when mixtures of sulfuric acid with either nitric or perchloric acid were atomized in the graphite furnace of an atomic absorption spectrometer. The mixtures apparently formed thermally stable compounds with the graphite, which were not removed by pyrolysis at temperatures up to 1100°C. During the subsequent atomization, volatile species were released and their absorption could not be compensated by the conventional deuterium lamp system. The absorption and emission spectra of the species formed in the furnace showed the presence of CS and probably COS, as well as bands appropriate to S₂, SO₂ and NS. The uncorrectable absorptions detected at the 303.8-nm nickel line, the 303.94-nm indium line, and the 304.40-nm cobalt line are thought to be caused by the fine-structure of an unknown molecular compound.