19
Instrument Operation
Before testing samples
Like most measuring instruments, cryoscopes need calibration against
standards. Your 4250 was calibrated at -408 m°C and -600 m°C at the
factory. The probe and calibration parameters are stored in parameter
RAM which is powered by an internal battery when the instrument
power is off or disconnected. Thus, when “Cryoscope Ready” is dis-
played, your 4250 cryoscope is calibrated and ready to run. However,
the calibration should always be verified during operation to be sure
that none of the parameters affecting calibration have changed (if recali-
bration is required, see Chapter 4).
Instrument operation in the following manner is recommended:
1. Remove the sample tube from the freezing chamber (see Figure 5,
Item 8).
2. Gently wipe the probe, stir/freeze wire, mandrel and the top of the
freezing chamber (in that order) with a soft, lint-free, non-ionic
paper tissue dampened with distilled water to remove anything that
might contaminate the sample to be tested. Be careful not to bend
the probe or stir/freeze wire.
3. Select a reference solution or NaCl standard with a freezing point
close to that expected for your unknown (Advanced Lactrol
®
530 is
recommended for milk). Swirl and carefully open an ampule of the
reference solution (or NaCl standard) selected.
4. Select a clean sample tube (see page 20, Repeatability Tips).
5. Pipette or measure a sample of the selected reference solution or
NaCl standard into the clean sample tube and place the tube in the
freezing chamber.
6. Press the START key.
If “I.D. #” has been enabled via the setup menu (see page 27), the
instrument operator will be prompted for a sample or user identifi-
cation number of up to 13 digits at this time from either the keypad
or optional barcode scanner.
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