Advanced Instruments 4250, User Manual

Page: 46 / 121

7. The rest of the test is completely automatic. The operating head will
lower the sample probe into the sample tube in the freezing chamber.
The fan will come up to full speed and the freezing chamber will
cool.
The sample temperature will follow the freezing curve shown in
Figure 1 and be displayed as soon as it falls below 0°C.
The 4250 will freeze the sample at a fixed crystallization point, fol-
low the plateau development, determine the freezing point, and lock
the result on the display and in the RECALL buffer.
NOTE If the STOP soft key is pressed while a test is in progress,
the test will be discontinued and the 4250 will reset itself for
the next test.
8. When the display reads “ Freezing Pt xxx mC ” (or xxx mH ), the test
is completed and results may be recorded.
9. Gently wipe the probe, stir/freeze wire, mandrel, and the top of the
freezing chamber (in that order) with a soft, clean, dry, lint-free paper
tissue after each test, to avoid contaminating the next sample. Be
careful not to bend the probe or stir/freeze wire.
10. Repeating steps 1-8, test two to four more aliquots of the same refer-
ence solution or standard to check repeatability and accuracy before
running tests on unknown samples. Follow the techniques recom-
mended on page 20, Repeatability Tips. When checking calibration or
repeatability with standards or reference solutions, it is usually best to
average the readings from three to five aliquots of each sample to
avoid error.
11. If the accuracy and repeatability on the reference solution (and/or cal-
ibration standards) are satisfactory, you may begin testing unknown
samples, using exactly the same test procedure as for the reference
solution and standards.
12. Always wipe the probe, stir/freeze wire, mandrel, and the top of the
freezing chamber with a soft, clean, dry, lint-free paper tissue after
the last test, to avoid having contaminating material dry on the probe.
24
Advanced
®
Cryoscope Model 4250 User’s Guide