Direct FexOy speciation in solid state materials by pulsed millisecond radio frequency glow discharge time-of-flight mass spectrometry

Abstract

Although glow discharge mass spectrometry (GDMS) is best known for its utility in trace element analysis, recent work demonstrates that the technique can also provide chemical speciation information. Previous reports outline approaches for the direct speciation of chromium and manganese oxides utilizing GDMS. As that work illustrates, different approaches to speciation are needed depending on the metal oxide under study. The present work extends the application of this technique to the direct speciation of three iron oxide species in solid state samples. The appropriate adjustment of parameters such as sampling distance, temporal regime, discharge gas pressure, pulse frequency, and duty cycle is essential to enable such speciation. For the iron oxides, species specific variations in ratios between Fe⁺ and FeOH⁺ signal intensities provide the ability to discriminate between FeO, Fe₂O₃, and Fe₃O₄. Iron–oxygen cluster generation correlates with oxygen abundance in the original sample as seen in these comparisons.