Novel headspace gas chromatographic method for determination of oxalate in oxygen delignification liquor

A novel headspace gas chromatographic (HS-GC) method is demonstrated for an indirect determination of oxalate in oxygen delignification liquors. A small volume (50-100 microL) of liquor sample is introduced into a sampling vial that contains 1.0 mL of 2 mol/L sulfuric acid. After removal of carbon dioxide (generated from carbonate in the acidic medium) by heating, the sample was mixed with a 0.5 mL of 0.02 mol/L potassium permanganate solution in a closed testing vial. At an elevated temperature (70 degrees C), the oxalate in the sample is rapidly converted to carbon dioxide by reacting with permanganate. The carbon dioxide in the headspace can be measured by gas chromatography with a thermal conductive detector. Using a multiple headspace extraction (MHE) measurement technique, the kinetics of formation of the carbon dioxide from the other organic species in the sample can be determined, and thus a correction can be made for minimizing the interferences. The present method is simple, accurate and can be easily automated.