Roche Diagnostics
30 Instructions for Use · Version 10.0
2 General description 9180 Electrolyte Analyzer
Measurement and calibration procedures
Measurement and calibration procedures
Measurement procedure
The 9180 Electrolyte Analyzer methodology is based on the ion selective electrode
(ISE) measurement to determine the measurement values.
u Measurement principle (p. 53)
There are six different electrodes used in the 9180 Electrolyte Analyzer: sodium,
potassium, chloride, calcium, lithium and a reference electrode. Each electrode has an
ion-selective membrane that undergoes a specific reaction with the corresponding
ions contained in the sample being analyzed. The membrane is an ion exchanger,
which reacts to the electrical charge of the ion. This causes a change in the membrane
potential, or measuring voltage, which is built up in the film between the sample and
the membrane.
A galvanic measuring chain within the electrode determines the difference between
the two potential values on either side of the membrane. The galvanic chain is closed
on one side by the reference electrode, reference electrolyte and the "open terminal".
The membrane, inner electrolyte and inner electrode close the other side.
A difference in ion concentrations between the inner electrolyte and the sample
causes an electro-chemical potential to form across the membrane of the active
electrode. The potential is conducted by a highly-conductive inner electrode to an
amplifier. The reference electrode is connected to ground as well as the amplifier.
The ion concentration in the sample is then determined by using a calibration curve
determined by measured points of standard solutions with known ion
concentrations.
Calibration procedure
A 2-point calibration is performed automatically every 4 hours in READY mode and
a 1-point calibration is automatically performed with every measurement.
An automatic calibration procedure is also performed shortly after power-on or reset.
A calibration cycle can also be initiated manually at times when no sample
measurements are performed.
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