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Yingtai: Analyze The Drying To Determine The End of Drying Method

Views: 365     Author: Site Editor     Publish Time: 2024-10-05      Origin: Site

Yingtai: Analyze the drying to determine the end of drying method

 

(a) Temperature convergence method product temperature is often used as an indicator to determine the end of drying, it is an indirect measurement. Temperature method using the dried product temperature and shelf temperature there is a thermal equilibrium between the determination. With the sublimation of moisture, the product temperature will gradually increase, when the product temperature and the shelf temperature is the same, indicating that the product's residual moisture is basically evaporated.

(B) vacuum method vacuum method is to use the correlation between the speed of pressure rise and the amount of residual moisture to determine the end point of freeze-drying. Usually think that when the pressure in the freeze-drying box is very low, and reached a steady state when the material is considered to have completed drying. However, the pressure in the freeze-drying box to reach a stable state usually takes quite a long time. It is generally believed that if the leakage rate of the freeze-drying box is small and constant, the relative rate of change of the pressure rise can be suggested by the end of the drying point. This is the current application of more to determine the end point of a method of drying.

(C) weighing method weighing method is the use of product weight loss rate and the relationship between the moisture content of the product to determine. In the drying process, continuously or periodically weighing the weight loss in the freeze-drying box or the amount of ice frozen on the condenser, until the weight loss rate tends to balance, you can determine whether the drying is over. For large-scale lyophilizer, weighing method produces a relatively large error, and for small lyophilizers this method is relatively simple, accurate, so this method is only suitable for laboratory lyophilizers.

(D) humidity method of alumina film moisture-sensitive components of the principle of moisture measurement is due to the porous aluminum oxide film is easy to absorb water vapor in the air, thus changing its own dielectric constant, so the capacitance value of the capacitor consisting of aluminum oxide as electrolyte will change with the partial pressure of the water vapor in the air, so the measurement of capacitance value, you can get the relative humidity of the air. At the end of the drying point, the partial pressure measured by the electronic water vapor sensor will suddenly drop. So this method can be used when the conventional product temperature response method does not give accurate information. In addition, residual gas analyzers have been used as a testing tool for freeze-drying pharmaceutical products. A residual gas analyzer is a small quadrupole mass spectrometer, and such systems typically include a quadrupole mass analyzer, a diffusion pump, one or more mechanical pumps, and a series of valves for sampling. The biggest disadvantage of the residual gas analyzer is its high price and the size of the equipment.

(v) Pulsed Nuclear Magnetic Resonance (NMR) NMR method is a relatively easy to determine the water content of the analytical means, through the study of the relaxation time of the proton can characterize the proton activity, can provide information related to the binding force and movement of water molecules. Basic Principle: The pulsed NMR technique is capable of quantifying the number of liquid protons in a sample below 0°C. Below 0°C, free water in the sample is frozen and contributes to the solid portion of the NMR signal, while bound water is often not frozen at -25 to -15°C. NMR spectroscopy can be used to observe and analyze structures directly in the solid state without destroying the specimen surface.


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