Freezing of aqueous solution in a simple apparatus designed for measuring freezing point

Freezing point depression (FPD) measurement can be used as a fast means of determining solute concentration of an aqueous solution in the laboratory and the data are useful in the process design of low temperature operations, e.g. freeze concentration and freeze drying, etc. It is desirable to have a cost-effective device for FPD measurement. Here, we describe a simple device for highly concentrated aqueous solutions. The characteristics of the freezing process of a small amount liquid (a few micro-liters) in this device, i.e. the effects of sample size, supercooling and location of measuring point, have been investigated. The reproducibility of the method has been found to be within +/-4% in a wide range of freezing points (-10 degrees C to 0 degrees C) for NaCl solutions. The solid entrainment in the ice formed prior to the freezing point being reached has also been estimated, and gives a distribution coefficient of 0.5. (C) 1997 Canadian Institute of Food Science and Technology.