Co-melting point of freeze-drying technology and measuring method thereof

Briefly:
The eutectic point test of the product was carried out using a eutectic tester designed and manufactured by Bo Yikang. The mechanism of this test method is to measure the eutectic temperature of the product by using a resistance method using a 1000 Hz AC power source by testing the change in resistivity.
Introduction:
The product that needs to be lyophilized is usually a solution or suspension pre-formed into water, so its freezing point is different from water. The water freezes at 0 °C, but the sea water is below 0 °C. Icing, because seawater is also an aqueous solution of many substances. Experiments indicate that the freezing point of the solution will be below the freezing point of the solvent.
In addition, the icing process of the solution is not the same as the pure liquid. The pure liquid such as water freezes at 0 ° C, the temperature of the water does not decrease, and the temperature does not decrease until all the water freezes, indicating that the pure liquid has a fixed knot. freezing point. The solution is different. It does not completely condense into a solid at a certain fixed temperature. At a certain temperature, the crystal begins to precipitate. As the temperature decreases, the number of crystals increases continuously until the solution is completely condensed. Thus, the solution does not condense at a certain fixed temperature. Instead, it condenses in a certain temperature range. The temperature at which crystals begin to precipitate when cooled is referred to as the freezing point of the solution. The temperature at which the solution is completely condensed is called the freezing point of the solution. The freezing point is the starting point of melting (ie, the melting point), which is the point at which the solution and the solvent melt together. So it is also called the eutectic or eutectic point. It can be seen that the freezing point and the eutectic point of the solution are different. The eutectic point is the temperature at which the solution actually solidifies completely into a solid.
It is clear that the concept of eutectic is important for freeze drying. Because lyophilized products may have substances such as salts, sugars, gelatin, proteins, blood cells, tissues, viruses, bacteria, and the like. Therefore, it is a complex liquid, and its freezing process is certainly a complicated process. Similar to the solution, there is also a temperature at which all of it actually condenses into a solid, that is, the eutectic point. Since freeze drying is carried out under vacuum. Sublimation drying can only be carried out under vacuum after the product is completely frozen. Otherwise, in the presence of some liquid, not only will it evaporate rapidly under vacuum, but the concentration of the liquid will reduce the volume of the lyophilized product; and the gas dissolved in the water will be under vacuum. It quickly pops up, causing the liquid to boil, causing the freeze-dried product to bubble or even emerge out of the bottle. This is what we don't want. To this end, the lyophilized product must be cooled to a temperature below the eutectic point at the beginning of sublimation, so that the lyophilized product is completely frozen.
During the freezing process, it is impossible to determine whether the product is completely frozen into a solid from the observation of the appearance; it is impossible to determine the structural state inside the product by measuring the temperature. The change in electrical properties is extremely useful as the product structure changes. Especially when the temperature is measured during freezing, we can know whether the freezing is in progress or has been completed. The resistivity will be very large after all freezing, so the solution It is ion conductive. When frozen, the ions will be fixed and cannot move, so the resistivity is significantly increased. The resistivity will decrease significantly when a small amount of liquid is present. Therefore measuring the resistivity of the product will determine the eutectic point of the product.
Bo Medical Kang's melting point measurement method introduction:
A pair of platinum electrodes were used and a temperature sensor was installed in the middle of the platinum electrode. The Pilot 2-4 pilot lyophilizer separator was started to cool the product to a temperature below -40 ° C, and then the frozen product was slowly warmed. The resistance is measured by the Bo Kang Kang eutectic tester. When the resistance suddenly decreases, the temperature at this time is the eutectic point of the product. The tester is powered by an alternating current because the direct current is electrolyzed and the entire process is recorded by the PC recording software.

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