Dynamic flash combustion

A key to elemental analysis is dynamic flash combustion, which creates a short burst of gaseous products, instead of slowly bleeding products out over several minutes. This feature is important because chromatographic analysis requires that the whole sample be injected at once. Otherwise, the injection zone is so broad that the products cannot be separated. 

Figure 27-8 Sequence of events in dynamic flash combustion. [From E. Pella, "Elemental Organic Analysis. I. Historical Developments," Am. Lab.

In dynamic flash combustion, the tin-encapsulated sample is dropped into the preheated furnace shortly after the flow of a 50 vol% O2/50 vol% He mixture is started (Figure 27-8). The Sn capsule melts at 235°C and is instantly oxidized to Sn02, thereby liberating 594 kJ/mol, and heating the sample to 1 700°-l 800°C. If the sample is dropped in before very much Oz is present, decomposition (cracking) occurs prior to oxidation, which minimizes the formation of nitrogen oxides. (Flammable liquid samples would be admitted prior to any 02 to prevent explosions.)... 

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