6875 Freezer/Mill
Page 21 of 42 SPEX® SamplePrep LLC DEC 2015
6.1 Adding Liquid Nitrogen Coolant (Cont’d)
Unlatch the lid and the gas cylinders will push it open. To unlock the latch, press down on the lid
and pull the top of the latch forward and down. Disengage the bottom of the latch and the lid
can be opened. The coil assembly is attached to the lid and will rise with it. The chamber gate is
on the right side of the coil housing. To lower the gate to insert a loaded vial for grinding, lift the
coil gate handle to the horizontal position and twist to align with the slot in the coil gate. Then
pull the coil gate to the right to open.
Note that there are three different sizes of vial that can be run in the 6875 Freezer/Mill: Large,
Mid-Size, and Small. Mid-Size vials must be run with a 6886 Adapter in the coil, and Small vials
must be run with a 6806 Adapter in the coil. Large vials do not need an Adapter. See Section 4.4
for details.
With the vial or vials (and adapter) in place, loosen the coil gate handle a turn or two
counterclockwise, align the handle with the slot, close the gate, and turn the handle clockwise
until the gate is in snug contact with the vial or vials. To lock the gate, fold down the gate handle
against the gate. Do not overtighten the gate, as this can crack the vial’s center section.
If the Freezer/Mill tub is empty, pour liquid nitrogen (LN) into the tub until it is approximately on
third full. Initially LN will boil off vigorously, but as the tub cools the boiling will subside. Add
more LN gradually, to avoid splashing and boiling over, until the LN level is approximately 2
inches below the rim of the tub. When boiling is subdued, push the lid down gently until the
bottom of the latch can be engaged. Pause if splashing becomes excessive. When the vapor
stream has subsided, open the lid again and top off the liquid nitrogen in the tub, filling it to the
mark on the inside wall of the tub. Insert a loaded vial or vials into the coil (if this has not already
been done), and tighten and lock the coil gate.
Press the Freezer/Mill lid closed and latch it. When the lid is closed and latched, further nitrogen
boiling will be visible as a stream of condensed water vapor (“fog”) from the vent in the rear of
the Freezer/Mill; this is normal. A grinding program can now be run, as outlined in Section 5.2.
6.2 Loading Samples into Freezer/Mill Vials
6.2.1 Introduction and General Recommendations
Start by choosing a sample that is typical of those to be ground on a regular basis. As a rule of
thumb, the sample pieces should be small enough to circulate inside the vial as the impactor
moves back and forth, and should take up no more than ⅓ to ½ the volume of the vial, with the
impactor in the vial. Typical sample sizes for the different sizes of Freezer/Mill vials are shown
below in Table 1.
In practice, the optimum parameters (sample weight and size, precooling time, grinding times
and number of cycles, impactor rate, etc.) are customized to match particular samples.
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