SPEX SamplePrep 6875D Operating Manual page 23

6.2 Manually Adding Liquid Nitrogen (Cont'd)
• Grind longer. (In Manual Fill mode, 30 minutes of actual grinding time is the maximum
recommended for one run, due to the liquid nitrogen capacity of the tub, but you can
top off the LN and repeat the run if needed.)
6.2.2 Size of Sample Pieces
The size of sample pieces is important. For uniform results in Small Vials, most samples should
be cut into pieces smaller than 1/4 inch (6 mm). Very tough samples such as fresh bone should
be cut smaller, down to 1/8 inch (3 mm). Samples can be cut proportionately larger for Mid-
Size and Large Vials. In any case, the size of the pieces should be controlled, and consistent
from sample to sample. There are several reasons for this:
• The more irregular the size of the sample pieces, the more difficult it is to predict the
results. Similar sized sample pieces produce a more uniformed grind.
• Thin fibers and films in particular can be very difficult to cryo-grind unless they are cut
into small pieces first. Wads of long fibers and crumpled balls of film take up extra room
and can be elastic, even at cryogenic temperatures.
• Tough samples in large pieces can be very difficult to grind, and in rare cases may
damage the vial. A large, wedge-shaped piece of bone or a tough polymer can act as a
wedge to push a moving impactor through the side of the polycarbonate tube.
6.2.3 Loading a Sample into a Vial at Room Temperature
Attach the end plug to one end of a center cylinder and insert impactor. Now load sample and
attached the other end plug to close vial. Shake the vial to make sure the impactor has room to
move back and forth.
6.2.4 Loading a Precooled Sample into a Vial and Keeping it Cold
Some samples must be kept cold prior to grinding, such as plant or animal tissue being
prepared for RNA extraction. When a sample is precooled and must be kept cold throughout
the grinding process, the loading procedure is more elaborate.
Attach the end plug to one end of a center cylinder. Then place the cylinder, end plug side
down in a shallow liquid nitrogen bath. The liquid nitrogen level should completely cover the
end plug and 1 inch up the side the center cylinder. The vial racks with the 6870L and 6870S
Accessory Packs can be placed in an insulated container to hold the vials upright during LN
chilling. At the same time, chill the impactor separately. As soon as the submerged end of the
vial is chilled add in the precooled sample and then the chilled impactor. Now carefully insert
the other end plug (which is at room temperature) into the open end of the cylinder. Do not let
the precooled sample touch the "room temperature" end plug. The vial can now be carefully
placed in the precooling chamber or the grinding Chamber.
1300-87052-1A, REV 1
SPEX SamplePrep LLC
6875D Freezer/Mill
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