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

Chemische Reaktionen bei der Atomisierung von Molybdän in der Graphitofen-AAS

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  • Mechanisms of Atomization and Chemical Reactions in Graphite Furnaces
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Zusammenfassung

Die chemischen Reaktionen bei der Atomisierung von Molybdän wurden mit Hilfe von GraphitPlattformen zusammen mit der Röntgen-Diffraktionsanalyse untersucht. Bei der Erhitzung von Molybdän [als wäßrige (NH4)2MoO4-Lösung] im Graphitofen werden drei Molybdänoxide (MoO2(s), MoO3(s) und Mo4O11(s)) bei relativ niedrigen Temperaturen (<1 500 K) gebildet. Wenn Molybdän von einer pyrolytischen Graphitoberfiäche atomisiert wird, zeigt die Veraschungskurve eine Absenkung der Extinktion im Bereich von 1200 bis 1800 K. Deshalb sollte bei Verwendung eines mit pyrolytischem Graphit überzogenen Rohres oder einer entsprechenden Plattform für quantitative Molybdänbestimmungen eine Veraschungstemperatur von <1 200 K benutzt werden. Nach der Veraschungsstufe wurden sowohl auf der pyrolytischen als auch auf der normalen Graphitoberfläche Mo(s), MoC(s) und Mo2C(s) gefunden. Bildung von Mo(g) durch direkte Sublimation von Mo(s) und durch Dissoziation von MoC(g) sind thermodynamisch günstige Reaktionen bei der betreffenden Temperatur.

Summary

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.

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Chakrabarti, C.L., Wu, S., Marcantonio, F. et al. Chemical reactions in the atomization of molybdenum in graphite furnace atomic absorption spectrometry. Z. Anal. Chem. 323, 730–736 (1986). https://doi.org/10.1007/BF00467067

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  • DOI: https://doi.org/10.1007/BF00467067

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