How often do I need to replace the solvent in the titration beaker of my Karl Fischer titrator?
The first and most obvious answer to this question is that the solvent should be replaced as soon as the sample no longer dissolves. This, however, is only one of the reasons for changing the solvent. A second less obvious reason applies in the case of two component reagent where the titrant contains iodine and the solvent contains all the other components necessary for the Karl Fischer reaction. One of these other components is sulfur dioxide and this can become depleted long before the dissolving capacity of the solvent is exceeded. As a general rule the solvent in these two component systems has an approximate water capacity of 7mg of water per mL of solvent. This means that in theory 40mL of solvent can accommodate 280mg of water before the solvent need be changed. As the typical titrant has a concentration of 5mg/mL, 280mg of water would require 56mL of titrant.
