RADIOMETER ABL800 FLEX, Справочное руководство

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1. Potentiometric measuring principles ABL800 FLEX Reference Manual
Reference electrode
Description The reference electrode is used in the measurement of pH and electrolyte
parameters and is located in the pH/Blood Gas module.
The reference electrode maintains a stable, fixed potential against which other
potential differences can be measured. The potential is not altered by sample
composition.
A fixed potential is maintained at the reference electrode by the following
equilibrium reactions:
AgCl
⇔
Ag + Cl
+
−
Ag + e
⇔
Ag
+
−
These reactions are possible because the electrode is made from a Ag rod coated
with AgCl to provide the Ag/Ag
+
equilibrium and determine the reference
potential.
The electrolyte solution acts as a salt-bridge
solution that maintains an electrical contact
between the coated Ag wire and the sample.
The solution is 4 M sodium formate
(HCOONa), adjusted to pH 5.5 with
hydrochloric acid.
The chloride concentration in the electrolyte
solution is adjusted in accordance with the
chloride concentration in the rinse solution,
to reduce Cl
−
exchange across the
membrane, thereby obtaining a more stable
potential.
The electrode is encased in the electrode
jacket: The rubber ring seals the electrode in
the jacket to prevent evaporation or leakage
of the electrolyte solution.
Electrode contact
Electrolyte
Ag rod coated
with AgCl
3-layer membrane
Electrode jacket
The membrane consists of three separate membranes:
Membrane Function
Inner To limit diffusion through the membrane and stabilizes the whole
membrane system.
Middle To prevent protein interference.
Outer To reduce the interchange of sample or rinse solution and
HCOONa solution.
Packaging
The E1001 reference electrode comes in a box with an insert explaining the
preparation of the electrode and its use.
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