SPI Supplies
22
SPI-DRY Critical Point Dryer
6.3
Tissue Preparation
It is suggested that the user consults the appropriate literature before deciding on any particular
techniques of sample preparation. A number of different methods are in use and the decision must be
made based on which technique will give the best results for a given material. It must be stressed that
the final result will depend almost entirely on the preparative technique carried out
BEFORE THE
SPECIMEN GOES INTO THE PRESSURE CHAMBER
.
The following technique suggested by Dr. A. Boyd of University College, London. The sequence of
operations outlined is very comprehensive. In many cases it may be possible to omit some of the stages.
With difficult specimens however, care taken in fixation and dehydration produces much improved
results.
The whole objective of the method is to obtain a specimen, which has been dried by the critical point
method. During the preparatory stages,
THE SPECIMEN MUST BE GIVEN NO OPPORTUNITY TO
DRY PREMATURELY. IT MUST BE KEPT WET AT ALL TIMES.
The complete sequence involves the following steps:
(a)
Washing
(b)
Fixation
(c)
Dehydration
(d)
Substitution with CO
2
miscible liquid
(e)
Substitution with CO
2
(f)
Heating to super-critical temperature
(h)
Pressure release
NOTE: If dehydration is done with acetone, step (d) is omitted because acetone is miscible with CO
2
.
