Why is oxygen used to convert carbon into carbon monoxide during thermal analysis?

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In the context of analytical chemistry, oxygen is used as a reactive gas during thermal analysis to facilitate the isolation of specific analytes from a sample matrix.1

When a test portion is rapidly heated in a furnace, oxygen is introduced to convert carbon into carbon monoxide and sulfur into sulfur dioxide. This process is a form of thermal evolution technique, which relies on heat to transform an analyte into a gaseous species, allowing it to be separated from the undissolved test portion. By converting these elements into volatile gases, analysts can effectively isolate them for further measurement or remove them to eliminate interferences.1