Chemical reactions in the atomization of molybdenum in graphite furnace atomic absorption spectrometry

Abstract

Chemical reactions in the atomization of molybdenum in graphite furnace atomic absorption spectrometry have been studied using graphite platforms for atomization along with X-ray diffraction analysis. When Mo [as an aqueous solution of (NH4)2MoO4] is heated in a graphite furnace, three molybdenum oxides: [MoO2(s), MoO3(s) and Mo4O11(s)], are formed at relatively low temperatures (<1,500 K). When Mo is atomized from a pyrolytic graphite surface, the charring curve of Mo shows a dip in absorbance in the temperature range 1,200–1,800 K. Hence, a charring temperature <1,200 K should be used for quantitative determination of Mo when a pyrolytically coated tube or a platform made of pyrolytic graphite is used. Mo(s), MoC(s) and Mo2C(s) have been found on both the pyrolytic and the regular graphite surface after the charring step is completed. Formation of Mo(g) by direct sublimation of Mo(s) and by dissociation of MoC(g) are all thermodynamically favourable reactions at the temperature considered.