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High Technology, Inc.
109 Production Road,
Walpole MA USA 02081
Document Number
OM-E-FC-360-30
Revision Level
Rev. 3
Prepared By
J.S. Bolio
Approved By
S. Titov
Effective date
8/15/2016
Operator’s Manual: HTI BioChem FC-360
Page 168 of 217
HIGH TECHNOLOGY, INC. PROPRIETARY AND CONFIDENTIAL
The ISE Module Calibration Cycle performs two successive calibrations. The slopes should be repeatable
within 1.5 mV/decade change; if not, a message error will be shown.
Typical slopes are approximately 55 mV/decade for Li+, Na+ and K+ and 45 mV/decade for Cl-.
In practice, electrode slopes may be higher than the ideally predicted value of 59.2 mV/decade at 25°
C. Higher operating temperatures, interfering ions and other factors can raise the observed slope
significantly.
The slope changes with temperature.
The slope of the electrodes is equal to (RT/nF) = 59.2 at 25° C, where R is the gas constant, T is the
temperature in degrees K, n is the valence of the ion, and F is Faraday constant. If all of the factors are
constant except T, one can calculate the ideal slope of the electrodes based on the temperature. Some
examples of predicted slopes vs. temperature are listed below.
Temp. (in deg. C) Slope (mV/decade)
20 58.2
22 58.6
24 59.0
26 59.4
28 59.8
30 60.2
32 60.6
If the module is calibrated at any temperature within its specification, and the same temperature is
maintained during sample analysis, no error in the measurement will occur. Errors will occur only when
calibration and sample analysis are performed at different temperatures.
As electrodes age, slopes will decrease. Lower limits for acceptable slopes are set at the lowest value that
insures good analyzer precision.
The values of slopes between calibrations performed successively (one after the other) should not differ by
more than 1.5 mV/decade for any of the channels, (Li+, Na+, K+, or Cl-).
The calibration frequency should be once every 8 hours. A calibration should be performed after each
Clean Cycle, or if the QC sample results do not repeatedly fall within the proper ranges. The analyzer will
flag ISE results after the 8-hour interval is exceeded. Additionally, QC materials should be run after each
calibration to ensure the accuracy of sample results.