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The Karl Fischer titration can be applied to a wide variety of substances. The differences in sample properties, especially their solubility, can influence the course of the Karl Fischer reaction. There are a number of ways to adjust the working conditions in order to enhance solubility and therefore enable a direct Karl Fischer titration of a sample. Many of these variations are described in this section.
- Fats, oils and long-chained hydrocarbons have limited solubility in methanol. Solubility can be improved by the addition of long-chained alcohols or chloroform to the working medium.
- Polar substances, like proteins, carbohydrates and inorganic salts are either insoluble or dissolve only slightly in organic solvents. Addition of formamide improves solubility or dispersion of these samples.
- With certain samples, methanol can cause interfering side reactions and should be replaced with other solvents.
- Acids and bases can alter the pH of the Karl Fischer system outside the desirable range and must be neutralized.
- Natural materials (soils, grains, etc.) release water slowly. Titration at 50 °C or in boiling methanol accelerates the dissolution of the sample and the subsequent extraction of water.
- Ovens are used to draw out moisture from solids that only release water at temperatures higher than 60 °C. The evaporated water is carried over into the titration cell by a dried inert gas.
If the working conditions of the titration are modified, the requirements of the Karl Fischer reaction must be considered and stoichiometry must be maintained.
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