Siemens Rapidlab 1200, Operator'S Manual, Page: 67 / 448

Rapidlab 1200 Operator’s Guide: System Overview and Intended Use 1-47
02087462 Rev. V
The measuring electrode contains platinum and glucose oxidase or lactate oxidase
in a binder, while the reference electrode is composed of Ag/AgCl. Two other
electrodes are also present. The counter electrode is a Pt (platinum) conductor that
ensures a constant applied potential. Another measuring electrode, without the
enzyme, determines interfering substances in the sample. The potential from
interfering substances is removed from the total differential measurement. A
microporous cover membrane separates the electrodes from the sample.
Figure 1-35 Glucose and Lactate Biosensor
A constant voltage, called a polarizing voltage, is maintained during analysis. In
the glucose sensor, glucose from the sample interacts with the glucose oxidase on
the surface of the measuring electrode to form hydrogen peroxide and gluconic
acid:
2 2
) (
7 12 6 2 2
) (
6 12 6
O H O H C O O H O H C
acid gluconic
GOX
glucose
+ + +
→
where GOX is the glucose oxidase.
The polarizing voltage is sufficient to cause oxidation of the hydrogen peroxide to
oxygen:
1 Glucose or lactate measuring electrode
2 Reference electrode
3 Interference measuring electrode
4 Counter electrode
5 Sample path