Gas phase titration

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Gas phase titration refers, generally, to any titration done in the gas phase. More specifically, it refers to a method for determining reactive species in the gas phase by reaction with an excess of some other gas, which acts as the titrant. Most commonly the gaseous analyte is ozone, which can be "titrated" with nitrogen oxide according to the reaction

O₃ + NO → O₂ + NO₂.

After the reaction is complete, the remaining titrant and the product can be quantified (e.g., by FT-IR); this also gives the amount of analyte present in the original sample.

Gas phase titration has two advantages over simple spectrophotometry. First, the measurement no longer depends on path length, since the same path length is used for the measurement of both the excess titrant and the product. Secondly, the measurement no longer depends on a linear change in absorbance as a function of analyte concentration (Beer-Lambert law). Finally, it is useful for samples containing species which interfere at wavelengths typically used for the analyte.