Medica EasyStat - Analyzer Calculation Methods

98
p r i n c i p l e s o f o p e r a t i o n / t h e o r y
r
A comparative method of measurement is utilized. First, the analyzer
measures the potentials developed when the sample is positioned
in the electrodes. Next, Calibrant A is positioned in the electrodes.
The difference in the two potentials is related logarithmically to the
concentration of sodium, potassium, calcium or hydrogen ions in the
sample divided by their respective concentrations in the Calibrant
solution. Since the difference in potentials and the concentration of
the sodium, potassium, calcium-or hydrogen ions in the Calibrant
solution are known, the analyzer can calculate the concentration
of the ions in the sample, in accordance with the Nernst equation,
rewritten as:
E
(Samp)
- E
(Cal A)
= S log (C
i
(x) / C
i
(s))
or C
i
(x) = C
i
(s)
*
10
^
((E
(Samp)
- E
(Cal A)
)/S)
E
(Samp)
= ISE potential developed in sample solution
E
(Cal A)
= ISE potential developed in the standard solution
S = slope calculated during calibration
C
i
(x) = Concentration of ion “i” in the sample
C
i
(s) = Concentration of ion “i” in the calibrant