NOVA BIOMEDICAL Stat Profile PRIME - Principles of Measurement; Measured Values

B-1
Appendix B
Appendix B
B Principles of Measurement
This section explains the Principles of Measurement for the
Stat Prole Prime CCS Analyzer.
B.1 Measured Values
Measuring Technology: Ten Planar Sensor Technology (Na,
K, Cl, iCa, pH, PCO
2
, PO
2
, Glucose, Lactate, Hematocrit)
in a MicroSensor Card
B.1.1 Sodium, Potassium, Chloride, and Ionized Calcium
Calculating Sample Concentration
Equation 1 links the voltage of the cell (E
m
) to the activity
of the ion. Activity is related to concentration (C) through
the activity coefcient in the relation a = f * C. The activity
coefcient is a function of ionic strength. Thus, Equation 1
can be rewritten in terms of concentration as follows:
E
cell
= E
o
+ S log a
o
- E
r
- E
j
Equation 1
E
cell
= E
o
+ S (log(f * C)
o
) - E
r
- E
j
Equation 2
Similarly, Equation 2 is rewritten:
(fC)
x
E = E
x
- E
std
= S log
_________
Equation 3
(fC)
std
The total ionic strength of whole blood is relatively constant
over the physiological range.
1
As a result, the activity
coefcients of sodium, potassium, calcium, and chloride
can be assumed to be constant. The internal standards
are formulated to reect the same ionic strength as that
of whole blood. Therefore, a given ion’s activity coefcient
can be assumed to be equal in the standard and sample.
The activity coefcient terms in Equation 3 cancel out with
these results: