Briefly: Bo Yikang has been committed to the R&D and production of small-scale, pilot-scale, production-type vacuum freeze-drying equipment. In the process of long-term customer service, it was found that the majority of freeze dryers use customers to understand the mechanism of freeze-drying, and how to explore and optimize the freeze-drying process of products should not be known. Especially for the parameters that are particularly important in the lyophilization process, the scientific principle and how to determine it are not clear. In view of the above situation, the eutectic point temperature, the eutectic temperature, the disintegration temperature and the glass transition temperature involved in the lyophilization process are specifically discussed.
Eutectic temperature
A mixed solution of several substances, during the freezing process, some components are crystallized at the beginning, and the concentration of the remaining solution changes. When a certain temperature or temperature region is reached, the liquid and the components in the formed solid are exactly the same. The solution at this time is called a eutectic solution, and the temperature or temperature interval is called the eutectic point of the solution or The eutectic zone, also known as the full cure temperature, is the highest temperature at which the product transitions from a liquid end to a solid state during cooling. The eutectic temperature is the highest temperature that should be reached during pre-freezing in the freeze-drying process. Generally, the pre-freezing process should be lower than the eutectic temperature of 10-20 °C.
Co-dissolution temperature
When the solid mixed solution is heated and melted, when a certain temperature is reached, the liquid begins to appear in the solid. This temperature is called the co-solvation point of the solution, or the melting temperature is started. It is the lowest temperature at which liquidity begins to appear in the solid state during product heating. The temperature of the frozen layer of the material must be lower than the co-melting point in one drying.
The measurement of the eutectic point is measured by electric resistance measurement, thermal differential analysis, direct observation by a cryogenic microscope, and numerical formula calculation. During the freezing process of the solution, the drift rate of the ions gradually decreases with the decrease of the temperature, and the resistance increases. As long as the liquid exists, the current can flow. Once all the freezing, the charged ions cannot move, and the resistance will suddenly increase. According to this principle. , the eutectic point of the solution is measured.
Collapse temperature (disintegration temperature)
The ice crystals in the material disappeared during lyophilization, and the space occupied by the ice crystals originally became holes, so the lyophilized layer has a porous honeycomb sponge structure. This structure is temperature dependent. When the solid matrix temperature of the honeycomb structure is high, its rigidity is lowered. When the temperature reaches a certain critical value, the rigidity of the solid matrix is ​​insufficient to maintain the honeycomb structure, the solid substrate wall of the cavity will collapse, and the original vapor diffusion channel is closed. This critical temperature is called the collapse temperature of the freeze-dried material. Or collapse temperature.
Glass transition temperature
When the temperature is lowered, the liquid state changes to a solid state, and there are two different states: crystalline and amorphous. In amorphous solid materials, the arrangement of atoms, ions or molecules is random. Since inorganic substances that have been accustomed to crystallization of molten substances during cooling are called glasses, other amorphous states are gradually referred to as glass states. Due to the stricter requirements in the lyophilization of pharmaceuticals, it is desirable that the drug be below the glass transition temperature during lyophilization. However, the glass transition temperature here does not refer to complete vitrification, because complete vitrification means that the entire sample forms a glassy state, and it is almost impossible to achieve a very high cooling rate for complete vitrification. The glass transition temperature of the lyophilization process refers to the glass transition temperature of the maximum frozen concentrate. Because the concentration of the remaining solution gradually increases with the precipitation of ice crystals during the freezing process, when a certain concentration is reached, the remaining water is no longer crystallized, and the solution reaches a maximum freeze-concentration state, and the corresponding temperature is called the maximum frozen concentrated liquid. The glass transition temperature.
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