RADIOMETER ABL800 FLEX, Reference Manual

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ABL800 FLEX Reference Manual 2. Amperometric measuring principles
General information,
Continued
The membrane is selective to the species A , allowing no other species but it to pass
through from the sample into the electrolyte solution.
Amperometric
method
(continued)
As an appropriate potential is applied across the electrodes, the species A is
reduced at the cathode according to the following reaction:
A + e
−
→
A
−
The reduction of A produces a flow of electrons, i.e. an electrical current.
To complete the electrical circuit an oxidation reaction where electrons are
released is necessary. Therefore species
X is oxidized according to the following
reaction:
X
→
X
+
+ e
−
The magnitude of the current flowing through the circuit is proportional to the
concentration of the species being reduced, in this case species
A . The analyzer
thereby automatically calculates the concentration of A in the sample.
The amperometric measuring principle is applied in the p O
2
, glucose and lactate
electrodes.
Calibration The electrodes are active elements and must be calibrated regularly as the signals
from the electrodes change with, e.g. age or deposits on the membrane.
Calibration relates the electrode signals during the calibration sequence to the
values of the calibrating solutions and must be performed at regular intervals so
that the accuracy can be constantly refined after inevitable minor changes in the
electrodes’ behavior.
Actual electrode condition is described by zero point and sensitivity and compared
with theoretical conditions for an "ideal" electrode. In addition to zero point and
sensitivity, an electrode condition is described by drift.
Calibration
material The following calibration materials are used:
Gas 1 and Gas 2: each gas has a precise composition
essential for determining the accuracy of the analyzer in
each
p O
2
measurement.
Calibration of the p O
2
electrode
Calibration Solution 1 Calibration of the
metabolite electrodes
2-3