Determination of oxalate by gas chromatographic measurement of carbon dioxide evolved from the photochemical decomposition of iron(III) oxalate

Oxalate over the range of 0.4 M to 1 × 10 −5 M can be determined with an accuracy of about 2% by injection of sample solutions into a photolytic cell containing an acidic solution of iron(III). Ultraviolet irradiation decomposes the iron(III) oxalate complex to iron(II) and carbon dioxide. The carbon dioxide then is purged from the cell in a stream of helium, dried, separated from other gases on a column of silica gel, and measured with a thermal conductivity detector. Interference from calcium, magnesium, thorium, aluminum, and several carboxylic acids is slight, while that from malonic. citric, formic, and tartaric acids is moderate. Strong ultraviolet absorbing species affect results by reducing the efficiency of photolysis.