OTF 5000/HS/LS-001/2/3/4 Iss 4 June 2012
31
3.7.2 FIXED TISSUE
Differences between tissues are much reduced after fixation. Cutting temperatures around -
10ºC to -15ºC are recommended, but some experimenting may be required. Ensure fixative is
rinsed off tissue before freezing.
4.1 DAILY CARE
Routine daily care consists of removing sectioning debris from the working area and brushing
debris & frost from the knife.
4.2 AUTOMATIC DEFROST CYCLE
Refer to section 2.1.6. The function of the automatic defrost cycle is to clear the evaporator
cooling fins of frost but without allowing the chamber or microtome temperature to rise above
0ºC. This ensures efficient refrigeration.
4.3 TOTAL DEFROSTING
It will be necessary to periodically defrost the entire cryostat to carry out cleaning and/or other
procedures. The frequency of this total defrosting will depend on how heavily the cryostat is
used; it may be as often as daily but is commonly once a month.
To initiate a total defrost:
1 Place a suitable container under the drain tube.
2 Turn off the cryostat.
IMPORTANT: If decontamination of the cryostat is required carry out the standard procedures
as practised in your laboratory at this point. Refer to section 4.8 for further details.
3 Remove the microtome knife (refer to section 2.2.2) and clean it (see section 4.4).
4 Remove the microtome from the chamber, the reverse of the installation procedure (see
section 1.2.5). Remove drain plug from base of chamber.
5 Place the microtome on the laboratory bench and clean it. Refit the rewind knob and rewind
the feed mechanism until the pointer is at the bottom on the indicator. Undo the two knurled
screws on the specimen arm and lift off the upper debris screen. Now remove the two small
screws which hold the microtome cover, using the Allen key provided. The cover can now be
lifted off. Allow the microtome to warm up completely and dry it off carefully.
6 The chamber interior can now be cleaned once it has thawed. Replace the drain plug.
7 Once the chamber and microtome have been cleaned and dried off, apply a little low
temperature oil to the threads of the knife clamp screws and feed screw, replace the cover
and re-install in the chamber (see section 1.2.5).
Make sure that the inside of the cryostat is perfectly dry before switching the refrigeration on.
Use a hair dryer if necessary. Note that the microtome requires no other routine maintenance.
4.4 MICROTOME KNIVES
GREAT CARE MUST BE EXERCISED WHEN HANDLING KNIVES
− knives must be stored in their boxes when not in use
− knives fitted to the microtome must be properly guarded
− particular care must be taken during cleaning and knife sharpening
Conventional microtome knives are usually made from carbon steel and will corrode in moist
conditions.
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