Distillation Technique

Distillation techniques involve co-distilling the water in a sample with a high boiling point solvent that is immiscible in water. Solvents commonly used are toluene, with a boiling point of 111.5 °C, or tetrachlorethylene, with a boiling point of 121 °C. The mixture is heated in an apparatus that condenses the vapors and collects the water in a graduated tube. Any evaporated solvent is condensed and returned to the mixture. Normally, the water volume is checked after 45 minutes and rechecked 15 minutes later. If the volume has not changed, then the procedure is terminated, the water collected is measured, and the moisture content is determined.

The disadvantages of the distillation technique are:

1. It was developed as a rapid method for quality control work, but it is not adequate for routine testing;

2. Any volatile compounds present in the sample (alcohol, glycerol, acetone) which are also miscible in water can evaporate along with the water causing errors in moisture content determination;

3. Care must be taken when utilizing toluene as a solvent because it is a fire hazard.