The usage process of laboratory freeze dryer is a systematic operation process. The following is a detailed description of the usage process:
1、 Pre preparation and sample preparation
1. Evaluation of sample suitability
-Select samples with a moisture content greater than 70% that are heat sensitive or prone to oxidation (such as enzyme preparations, bacterial strains, medicinal materials, etc.), and avoid direct freeze-drying of high sugar/high protein samples (protective agents such as trehalose need to be added to prevent structural collapse).
-When packaging, control the sample thickness to be ≤ 10mm (liquid samples should not exceed 1/3 of the container depth), use shallow trays or penicillin bottles to evenly spread them, and avoid stacking that affects heat transfer efficiency.
2. Container sterilization and cleaning
-All containers that come into contact with the samples must be sterilized under high temperature and pressure before drying, and aseptic operations must be completed in a biosafety cabinet [^ 1 ^].
-Equipment inspection: Confirm that the temperature of the cold trap has dropped below -50 ℃, the oil level of the vacuum pump is at 1/2~2/3 of the window, and the sealing ring is intact without damage.
2、 Pre freezing stage: key control of ice crystal formation
1. Selection of pre freezing method
-Built in pre freezing machine: Place the sample in the cold trap tray, activate the pre freezing mode, and set the temperature 5-10 ℃ below the eutectic point of the sample.
-External pre freezing: Freeze the sample in an ultra-low temperature refrigerator (-80 ℃) or liquid nitrogen for 2-4 hours until the center of the sample freezes (with a crisp sound when tapping the container).
2. Anti melting measures
-Insufficient pre freezing can cause the sample to melt and bubble during the drying stage. It is necessary to monitor the surface temperature of the material using an infrared thermometer to ensure that the freezing depth meets the standard.
3、 Vacuum freeze-drying: precise control in stages
1. Sublimation drying (primary drying)
-Start the vacuum pump, draw the vacuum degree to 10~50Pa, slowly raise the temperature to -20~-10 ℃ (below the eutectic point), and continue for 2~24 hours (adjusted according to the thickness of the sample). At this stage, remove more than 90% of free water and observe that the frost layer in the cold trap no longer thickens, which is the endpoint.
2. Analysis of drying (secondary drying)
-Gradually raise the temperature to 0-30 ℃ (protein ≤ 25 ℃), maintain a vacuum degree of 5-10 Pa, and promote the desorption of bound water. Determine the endpoint through weighing method: the difference between two consecutive weighings is less than 0.1%.
4、 End drying and sampling standards
1. Break the vacuum and seal
-After turning off the vacuum pump, slowly introduce nitrogen gas to restore normal pressure, quickly remove the sample and seal it (sealed with penicillin bottle stopper or aluminum foil bag vacuum packaging), and store it at 4 ℃ or -20 ℃ environment.
2. Equipment reset and cleaning
-After defrosting and draining, wipe the cold trap and shelf with 75% alcohol, check the oil quality of the vacuum pump (replace if cloudy), and record the operating parameters.
The use of laboratory freeze dryers is a combination of scientific prediction and precise control. Strictly following standardized procedures can significantly improve the retention rate of sample activity (up to 92% or more), while reducing the risk of equipment failure.