Freeze drier drying chamber

Thin slices of tissue are placed in clean plastic petri dishes, the loose fitting lids replaced and the dishes inserted into the chamber of the freeze drier. Blood specimens can be poured directly into the dish. It is important that the tissue be thoroughly frozen prior to evacuating the chamber. The time required for complete drying of the sample depends on the nature and weight of the material and the type of equipment employed. Drying is usually completed in 12—48h. The dried tissue is not susceptible to decay and can be stored at room temperature in sealed plastic bags. 

Shortly after we had run this comparison study, our own aged freeze-drier collapsed into obsolescence. In order to make this method work, the freeze-drier must be specially constructed, without resin in the vacuum chamber and with traps placed in the vacuum line to prevent the back-diffusion of oil vapors from the pump to the vacuum chamber. While we have been awaiting the rejuvenation of our own instrument, rebuilt to these specifications, Michael McKinnon, of our laboratory, has developed a variation of the Russian evaporation method. In this method, as in the freeze-drying method, the great problem is avoiding contamination. Fortimately, when contamination does occur, it seems to affect an entire batch of samples. It is therefore possible to detect the contamination by the judicious use of standards. This method gives values for DOG of the same order as the lowest freeze-drying values or the Sharp (27) direct injection values. 

Aliquots of 1 ml of each model solution were placed in 3-ml glass vials, frozen at — 20°C, and quenched with liquid nitrogen before freeze drying. The freeze-drying process lasted 48 h. A Heto-Holten A/S, cooling trap model CTllO freeze drier (Heto Lab Equipment, Denmark) was used, operated at — 110°C with a chamber pressure of 4 X. 10 mbar. After freeze... 

Place freshly harvested plant leaf samples in labeled freeze-drier bags. Close the bags with paper clips then place the samples in a -80°C freezer see Note 2), and leave until frozen (longer than 6 h). Transfer the bags to a freeze-drier, evacuate the chamber, and freeze-dry overnight or until the samples are dry see Notes 3 and 4). At this point the leaves should be uniformly brittle. 

The chamber temperature on the freeze drier can be left at ambient (in fact, cooling the sample chamber increases the drying time). 

Spillages during dispensing are often overlooked since liquid product is invariably transparent. However any spilled liquid on the freeze-drier shelf will dry to form a thin, friable layer of powder which will be readily disseminated from the chamber when the vacuum is released and the product batch removed. 

Stoppered vials can be left in the chamber and exposed to a sterilising vapour in order to decontaminate the outside of the vials before their removal from the freeze-drier. In this laboratory we have been able to demonstrate that formaldehyde vapour will not permeate stoppered vials which contain freeze-dried samples. 

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