Determination of sugar surface moisture

Starting with a modified procedure for the Karl Fischer titration method with formamide as solvent, in which consumption at a constant rate in the blank test is eliminated, the authors examine a number of methods for determination of sugar surface moisture. To avoid that the obtained values comprise too the water occluded in the interior of the crystals the sample has to remain undissolved as far as possible.

The titration in formamide saturated with sucrose requires a relatively long period of time because of the high viscosity of the solution. With a solution containing a smaller concentration of sucrose, surface moisture values can be obtained by extrapolation, which however leads to varying results according to the reaction conditions.

The best and most precise process is titration in methanol saturated with sucrose. As in total water determination, the results are largely independent of quantitative proportions and reaction conditions.

A rapid method is given in which lower consumption of the Karl Fischer reagent obtained by reducing the reaction time compensates for the higher consumption caused by the blank test. The results are identical to those obtained in the precise procedure within experimental error.