RADIOMETER ABL800 FLEX Reference Manual

ABL800 FLEX Reference Manual 1. Potentiometric measuring principles
pCO
2
electrode, Continued
Nernst equation
(continued)
The pH value is related to the partial pressure of CO
2
in the sample by the
following equation:
2
CO2
-
3
a
CO
HCO
log +pK = pH
α ×p
c
where:
pK
a
= −log K
a
, the equilibrium constant for the dissociation of carbonic acid in
water
α
CO
2
= solubility coefficient for CO
2
in water
The bicarbonate concentration
[
]
HCO
3
-
is so large compared to
[
that it can be
considered constant. At constant temperatures
]
H
+
α
CO
2
is also constant. So the
equation can be simplified to:
pH = K' -log CO
2
p
where:
K' is a constant incorporating the equilibrium constant for carbonic acid (K
a
), the
bicarbonate concentration, and the solubility coefficient
α
CO
2
.
2
3
CO
HCOH
−+
×
=
cc
K
a
is the equilibrium constant for carbonic acid.
pCO
2
of the sample is then calculated from the equation above.
Designation
The following symbols are used:
pCO
2
(Gas1),
pCO
2
(Gas2)
= Pressure of CO
2
in Gas 1 or Gas 2, respectively
FCO
2
(Gas1),
FCO
2
(Gas2)
= Fraction of CO
2
in Gas 1 or Gas 2, respectively
B
Gas 1 or 2
= Pressure inside the measuring chamber during a
measurement on Gas 1 or Gas 2 respectively
pHO
2
= Water vapor pressure (6.2751 kPa at 37
o
C)
E(CO
2
,Gas1),
E(CO
2
,Gas2)
= Potential of the
pCO
2
electrode from a measurement on
Gas 1 or Gas 2, respectively
Sens(
pCO
2
,theo)
= Theoretical (absolute) sensitivity of the
pCO
2
electrode
at 37
o
C
Sens(
pCO
2
,prev)
= Relative sensitivity of the
pCO
2
electrode from the
previous 2-point calibration
Continued on next page
1-15

RADIOMETER ABL800 FLEX Specifications

General

Brand	RADIOMETER
Model	ABL800 FLEX
Category	Measuring Instruments
Language	English