Advanced Instruments 4C3, User Manual

Page: 66 / 139

C. Standards and controls
To be accurate, all measurements ultimately must be referred to
highly reliable independent standards. Advanced cryoscopes are
calibrated with standards consisting of stable sodium chloride solu-
tions of known freezing points which bracket those of the expected
unknowns. These standards are related to the most fundamental
work on freezing points of dilute solutions published and are trace-
able to the National Institute of Standards and Technology (former-
ly the National Bureau of Standards).
However, the most important cryoscope determinations are made,
not on sodium chloride, but on complex biological solutions. How
accurately they determine the freezing points of precisely-known
concentrations of sodium chloride solutions, therefore, is only one
measure of cryoscope accuracy. Another measure should involve
determinations on solutions or controls formulated to synthesize
biological solutions.
Please check with your associations and regulatory bodies for their
guidelines and/or control requirements.
D. Maintenance of standards
Doubts about the accuracy of standards destroy confidence in the
accuracy of the test. The Advanced cryoscope standards are spec-
ified to be within very close tolerances. Several of the sodium
chloride based reference and calibration solutions designed for the
Advanced cryoscopes are sealed in glass ampules to insure against
any possibility of alteration during transit or storage. However, we
recommend that you test samples from each newly-received lot and
maintain records of your test results on cryoscope standards for ref-
erence.
44
The Advanced
®
Model 4C3 User’s Guide