Sample eutectic point detection in freeze dryer

The so-called eutectic point refers to the temperature at which the material completely freezes into ice crystals in solution.

For freeze-drying technology, the determination of the eutectic point is very important and is the main basis for formulating the freeze-drying curve. The product must be frozen to a temperature below the eutectic point during pre-freezing, and the product cannot exceed the eutectic point temperature during sublimation. Therefore, the eutectic point temperature is also the highest allowable temperature in the pre-freezing and sublimation stages of the product.

The commonly used method for measuring the eutectic point is the resistance method. During the freezing process of the solution, the eutectic point is determined by measuring the change of resistivity in the solution with temperature. The conductivity of the solution belongs to ionic conduction. With the freezing of the solution, the ions are gradually fixed, and the resistance of the solution will gradually increase. When it is completely frozen into a solid, the resistance will suddenly increase. crystal point.

The resistance method is only a rough method. There is a special eutectic point tester for the measurement of the eutectic point of the product. At the same time, the eutectic point can be accurately measured by means of a freeze-vacuum drying microscope, DSC, DTA, and other methods. Considering the preparation of equipment and the operability of detection methods, the pre-freezing temperature is generally set below the eutectic point of 5°C. In general, resistance method measurement can be applied.

The level of the eutectic point is related to the composition and concentration of the solution. Changing the composition and concentration of the solution can change the eutectic point of the solution. Since products with a high eutectic point are easy to freeze-dry, the eutectic point temperature of the product can be increased by changing the composition and concentration of the product.

The most critical condition in the freeze-drying process is to control the temperature of the sample to be kept at 10-15°C below the eutectic point temperature, so as to ensure that the sample does not melt and maintain the microporous structure and physical and chemical properties intact.