Several methods exist for the determination of water in vegetable oils: loss on drying, reaction with calcium hydride, Karl Fischer titration (KFT), Fourier Transform Infrared (FTIR) and Raman spectroscopy as well as dielectric measurements. Among these, KFT is certainly the method of choice when trace amounts of free, emulsified or dissolved water have to be accurately determined in a short time.

KFT is based on the stoichiometric reaction of water with iodine and sulfur dioxide in the presence of a short-chain alcohol (R` = CH3, C2H5) and an organic base (RN). Volumetric KFT is applied to samples that contain higher water content—from approximately 1% up to 100%; the coulometric technique is ideally suited for samples with smaller water content—in the range of a few µg/g. In the volumetric KF technique a titrating agent containing iodine is added directly to the sample via a buret. In contrast, in coulometric KFT iodine is generated electrochemically from iodide in the titration cell. In both cases iodine reacts with the water in the sample. Once all the available water has reacted (equivalence point), the indicator electrode detects the first excess of iodine and the KFT stops. The amount of water is calculated by measuring the titrant consumption (volumetric KFT) or the electric charge needed for the oxidation of iodide to iodine (coulometric KFT).

The selectivity and absolute nature of KFT methods make it ideally suited for automation—enhancing sample throughput and improving accuracy, particularly when different determination methods for different types of samples are required.

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