ABL90 FLEX reference manual 5. Sensors and optical system
5-37
A constant polarization voltage is applied to the electrode chain. The current
through this chain is measured by an amperemeter.
Glucose or lactate molecules, in solution, are transported across the outer layer
of a multilayer membrane system. The enzymes glucose oxidase or lactate
oxidase, immobilized between the outer and inner layers, converts
glucose/lactate according to the following reactions:
Glucose: Glucose + H
2
O + O
2
Gluconic Acid + H
2
O
2
Lactate: Lactate + H
2
O + O
2
pyruvate + H
2
O
2
The oxygen for this reaction is supplied by the membrane system as well as by
the oxidation of H
2
O
2
at the platinum anode.
The H
2
O
2
produced by the enzyme reaction is transported across the inner
membrane to the platinum anode.
When a potential is applied to the electrode chain, the oxidation of H
2
O
2
produces an electrical current proportional to the amount of H
2
O
2
, which in turn
is directly related to the amount of glucose/lactate.
H
2
O
2
2H
+
+ O
2
+ 2e
–
At the counter electrode a reduction process, consuming electrons will occur:
1) H
2
O
2
+ 2e
-
2OH
-
(This process consumes excess H
2
O
2
not consumed in the reaction
above.)
2) ½O
2
+ H
2
O + 2e
-
2OH
-
(This process consumes excess O
2
not consumed in the reaction above.)
3) 2H
2
O + 2e
-
H
2
+ 2OH
-
(This process can also occur at the cathode.)
Any of these three reactions at the cathode will serve to neutralize the protons
generated in the second reaction, so the total change in acidity is caused by the
gluconic acid/pyruvate only.
Measuring
process
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