PP2000/PP2000T Sample Freezing
| The transfer device is used to transfer frozen samples under vacuum from the freezing device to the preparation chamber. The design and ease of use of the transfer device is crucial to the success of the cryo preparation procedure and the PP2000 transfer device has the following significant features: |
Transfer device. From right to left: shuttle, stub and sample, plastic thermal break, rod, vacuum chamber with lid
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| Sample freezing process The liquid nitrogen slusher is a small vacuum chamber with an inner insulated beaker for holding liquid nitrogen. The chamber has a vacuum port connected to a 90 l/m rotary pump. For convenience the slusher is mounted into the instrument trolley. Freezing in nitrogen ‘slush’ gives a faster cooling rate than can be achieved by plunging into normal liquid nitrogen. The use of nitrogen slush avoids the ‘Leiden’ effect in which an insulating gaseous layer is formed around the sample, preventing rapid cooling rates. Please note that it is possible to use faster more specialised freezing techniques (e.g. metal mirror, Propane plunging). In this case, the sample can be transferred onto the standard PP2000 stub and shuttle under liquid nitrogen. The sample, mounted on the shuttle, is plunged into nitrogen slush and allowed to equilibrate. The shuttle can then be retracted under vacuum into the sample transfer device and transferred into the PP2000 / PP2000T via the air-lock gate valve.
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| 1. The sample is plunge frozen in Nitrogen slush. |
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2. The sample freezing device in the plunged position |
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| 3. The transfer device after freezing ("slushing" device is in the background). Note shuttle with stub and sample held under vacuum within the inner vacuum chamber during transfer. Lid is secured by vacuum and by a simple to operate screw clamp |
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