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Validation of the Karl-Fischer method for determination of water in waste materials

Validatie van de bepaling van het watergehalte met behulp van Karl-Fischer titratie (NEN 5871)


An interlaboratory test was carried out to validate the Karl Fischer method for to determine free water and water of hydration in waste materials. This method is described in a draft standard NEN 5871. The aim of the interlaboratory test was to obtain information about the precision (repeatability and reproducibility) of the method and to check whether the draft standard requires some modifications. Eight laboratories participated in the interlaboratory test. The five materials tested were fixing-bath, aqueous cutting oil, used oil which was untreated, a mix of water/ethanol/acetone and sodiumtartrate-dihydrate (as reference material). It was found that 1) the repeatability and reproducibility depend on the level. Both statistical values increase with higher values of water content. 2) the mean value of the water content does not differ significantly from the adjusted values. 3) only two out of eight laboratories measured a water content in sodiumtartrate-dihydrate (reference material) similar to the certified value. 4) when the water content of waste is used for the conversion to its dry weight, one should take into account the fact, that low concentration of dry weight lead to imprecize results. The relative error of dry matter content increases with lower values of dry matter and higher values of water content.

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