Rapidlab 1200 Operator’s Guide: System Overview and Intended Use 1-31
02087462 Rev. V
Using an established convention, the activity of ions that are measured by sensors
can be expressed in terms of concentration. This convention contains the
assumption that the normal ionic strength of blood plasma water is 160 mmol/kg.
3
Because ionic strength is the primary variable affecting the activity coefficient of
ionic species in solution, controlling the ionic strength of calibrating solutions to
160 mmol/kg sets the activity coefficients of ionic species in the calibrating
solutions equal to those of blood plasma water at sample ionic strengths close to
normal. Both calibrations and the expression of measured quantities may then be
made in units of concentration instead of activity.
4
Reference Sensor
The reference sensor for the 1200 systems works with certain measuring sensors
in the measurement module to create an electrochemical cell. The reference
sensor provides a fixed potential, which is independent of analyte activity. The
system compares the fixed potential of the reference sensor to the measured
potential from the following sensors:
Sensor System
pH 1240, 1245, 1260, 1265
Na
+
1260, 1265
K
+
1260, 1265
Cl
-
1260, 1265
Ca
++
1260, 1265
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