Karl Fischer ROTI^®Hydroquant Working Medium K

There are two established Karl Fischer methods of calculating the water content of a substance: Volumetric analysis and coulometric analysis.

Which method is chosen depends primarily on the water content that the sample is expected to have. Making the right choice is vital for obtaining reliable and reproducible results. Carl ROTH offers compatible reagents for both of these methods.

Karl Fischer volumetric analysis is recommended if the water content of a sample ought to be between 0,1 % and 100 %. Volumetric analysis is performed by measuring the amount of Karl Fischer reagent that needs to be added to a substance until the end point of the titration has been reached. In alcoholic solutions, water reacts 1:1 with iodine in the presence of sulphur dioxide. Methanol and sulphur dioxide form an acid ester that is neutralised by the base (e.g. imidazole, hereafter referred to as "RN" for simplicity).

CH₃OH + SO₂ + RN → [RNH]SO₃CH₃

In the titration process, iodine is added which reacts with water to be reduced to colourless iodide:

[RNH]SO₃CH₃ + H₂O + I₂ + 2 RN → [RNH]SO₄CH₃ + 2 [RNH]I

This reaction continues until there is no water left. The end point is determined by a change in colour due to a surplus of iodine and measured using a potentiometer.

Table illustrating the uses of Karl Fischer ROTI^®Hydroquant volumetric reagents:

Single-component Reagents

Single-component reagents contain all the substances required for the Karl Fischer reaction in a single solution. They are easy to use and provide for a high level of flexibility when choosing a solvent for the sample type. The high reactivity of the components means that the titre for single-component reagents must always be determined before titration is carried out. Reactions with standard reagents containing methanol are not possible for samples that contain aldehydes or ketones, as the methanol will react with them to produce extra water in a secondary reaction. Carl ROTH offers methanol-free reagents that are suitable for substances containing aldehydes and ketones.