5.0
OPERATION
5.04 Filling the Tub with Liquid Nitrogen (Cont’d)
To assist in pre-cooling the vials, you might wish to place a vial in the coil, and two others in the
pre-cooling slot (Diagram “C,” item RO), before filling the tub with liquid nitrogen.
5.05
Loading the Vial
Pick a sample typical of those you will be grinding. For a polymer, measure out 1 to 2 grams, or
for bone and tissue samples (plant or animal), perhaps twice that much. Keep in mind that in
practice, the various parameters (sample size, pre-cooling time, grinding times and cycles, etc.)
are customized to match particular samples. Typically, the correct amount of sample will take
about 1/3 of the vial volume (with impactor in vial).
If the sample can be handled at room temperature, assemble the center cylinder and blunt end-
plug of a 6751 Vial (see Page 4). Add the sample and impactor to the vial, and close it with the
flanged end-plug. Shake the vial to make sure the impactor has room to move back and forth.
If the sample is cold, and must be kept cold throughout the grinding process, the procedure is
more elaborate. Assemble the center cylinder and blunt end-plug, as above, then chill the end-
plug and about an inch of the cylinder in a shallow liquid nitrogen bath. At the same time, chill
an impactor. The vial rack that comes with the 6750 Freezer/Mill can be placed in an insulated
container and used to hold the vials upright during chilling. As soon as the submerged end of the
vial is chilled, drop in the cold sample and the chilled impactor. (Always wear insulated gloves
when handling chilled vial components directly!) Now carefully insert the other end-plug, still
warm, into the warm end of the cylinder. The vial can now be carefully placed in the mill, or
submerged in a liquid nitrogen bath outside the mill, as long as you are careful not to let the
sample touch the warm end plug before it has cooled down. Very important: never force an end
plug (warm or cold) into a cold polycarbonate cylinder. Polycarbonate shrinks when chilled,
and can crack if stressed. When you follow this procedure for loading cold samples, if the
cylinder has cooled to the point where the end-plug fit is too tight, warm the end of the cylinder
before inserting the end-plug.
A variant of the above technique can be used to grind very small samples with the open pre-
chilled vial upright. Place the sample on the chilled end-plug and add a small amount of fluid
such as an extraction medium or water. The frozen fluid will bulk up the sample enough so it
will circulate in the vial during grinding.
Before loading the vial in the mill, put on cryogenic gloves. Unlatch and lift the lid of the mill,
and open the coil gate. Now pick up the vial with your gloved hand or the Extractor (page 17),
and insert the vial in the coil. If you have additional vials you wish to pre-cool, pick them up the
same way and insert them in the pre-cooling slot in the coil housing. Check the liquid nitrogen
level and top it off if necessary. Gently press the Freezer/Mill lid closed; the coil gate will shut
automatically, and the coil gate handle will retract into the tub. If the lid resists closing, make
sure the vial is inserted all the way in the coil. You are now ready to begin a programmed
grinding cycle.
Page 15 of 28
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