Refrigeration – Storage of solidified or liquified gas – Including cryostat
Patent
1994-05-31
1995-11-28
Kilner, Christopher
Refrigeration
Storage of solidified or liquified gas
Including cryostat
62 555, F25B 1900
Patent
active
054697123
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device for dehydrating and/or embedding samples, especially at temperatures between +20.degree. C. and -120.degree. C., in a sample container at a thermostatically regulated temperature in a Dewar vessel containing liquid nitrogen.
For rapid "immobilization", samples for microscope or electron-microscope investigations are frequently frozen extremely rapidly. Subsequently, the ice contained in the samples is to a large extent removed at temperatures between -80.degree. C. and -120.degree. C. either by polar solvent (eg. methanol: "Cryosubstitution", in this connection cf. inter alia patents DE 29 44 484 C2 or DE 29 44 464 or respectively H. Sitte, ZEISS MEM 3, 25-31, 1984 or H. Sitte et al, GIT Laboratory Medicine, 10, 199-208, 1987, further literature therein) or under vacuum or respectively by reduction of the water vapor partial pressure ("Freeze-drying": in this connection, cf. inter alia patent: DE 27 39 796 or respectively L. Edelmann, Microscopy Vienna, 35, 31-36, 1979, as well as L. Edelmann, Scanning Electron Microscopy, IV, 1337-1356, 1986, further literature therein), so that subsequently the dried samples can be embedded in paraffin or in a suitable plastic material for a subsequent section preparation. An alternative to this process is offered by the "PLT method" (PLT stands for "Progressive Lowering of Temperature; in this connection, cf. inter alia E. Carlemalm et al, J. Microscopy, Oxford 126, 123-143, 1982; further literature references therein), in which the samples are in the first instance chemically fixed, for example in an aldehyde solution, and subsequently cooled during their dehydration in polar media (eg. acetone or methanol) in each instance to that extent to which the freezing point of the mixture falls. The embedding in this case also takes place by UV polymerization of a monomer formulation at temperatures between -30.degree. and -70.degree. C. Both for cryosubstitution and for the PLT method, and also for the freeze-drying, systems have been developed in which in order to reach the required low temperatures and in order to generate a cryosorption vacuum, use is made of liquid nitrogen (hereinafter referred to as LN2). In these systems (cf. cited literature) in accordance with the prior art the containers provided to dry the samples are disposed either in the neck of a Dewar vessel or in its downwardly extended interior; in this case, the LN2 cooling takes place in the Dewar neck indirectly by the progressively formed gaseous nitrogen (hereinafter referred to as GN2) or by removal of heat via interposed solid bodies or in the interior of the Dewar vessel by direct contact with LN2.
A major disadvantage of such systems resides in that each one of these costly arrangements, which must have not only the Dewar vessel to receive the LN2 but also at least one of the control loops for the thermostatic control of the sample temperature as well as monitoring systems to display the LN2 filling level and warning systems to display an excessively low LN2 filling level, is suitable only for one of these low-temperature methods for drying frozen objects, which, in addition, must frequently be carried out alternately on a comparative basis. Thus, there is frequently a requirement to acquire not only a system for cryosubstitution and/or PLT incubation but also an apparatus, equipped similarly in a costly manner, for freeze-drying, if the intention is to carry out competent comparative investigations in this sector of science.
The object of the present invention is to provide an arrangement which is suitable for a plurality of processes.
According to the invention, this object is achieved in that there is disposed in the Dewar vessel a stationary metal cooling surface which is fixedly connected to the latter and is cooled by liquid nitrogen, and in that the sample container which is releasably insertable into the Dewar vessel, exhibits a contact surface which is complementary to the cooling surface and which rests on the stationary cooling surface when the sample con
REFERENCES:
patent: 4232453 (1980-11-01), Edelmann
patent: 4306425 (1981-12-01), Sitte et al.
patent: 4723420 (1988-02-01), Sitte
H. Sitte, Zeiss, MEM 3, 1984, pp. 25-31.
Carlemalm et al., "Practical Methods in Electron Microscopy", Journal of Microscopy, vol. 126, Pt 2, May 1982, pp. 123-143.
L. Edelmann, "Freeze-Drying of Chemically Unfixed Biological Material for Electron Microscopy", Mikroskopie, Vienna, 1979, pp. (35), 31-36.
L. Edelmann, "Freeze-Dried Embedded Specimens for Biological Microanalysis", Scanning Electron Microscopy, IV, 1986, pp. 1337-1356.
E. Carlemann et al., "Low Temperature Embedding", The Science of Biological Specimen Preparation, 1986, pp. 147-154.
H. Sitte et al., "An Instrument for Cryosubstitution And Low Temperature Embedding," GIT Laboratory Medicine, vol. 10:199-208, (1987).
Edelmann Ludwig
Haessig Helmut
Kleber Heinrich
Lang Anton
Neumann Klaus
Kilner Christopher
Leica AG
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