Rapid Lab Systems measuring principle

Agenda Sensor/Electrode Location Measuring principles The potentiometric measuring principle Reference electrode pH electrode Electrolyte electrodes pCO2 electrode The amperometric measuring principle pO2 electrode Metabolite electrodes

Location The Sensors are placed in the sensor modules easily accessible under a window on the front of the analyzer

Two measuring principles The potentiometric measuring principle is used for The amperometric measuring principle is used for pH, pCO2, cK+, cNa+, cCa2+, cCl– pO2, cGlucose, cLactate

The potentiometric measuring principle Electrodes measure a change in voltage due to a change in ion concentration across a membrane pH, pCO2, cK+, cNa+, cCa2+, cCl– V Voltmeter Reference electrode Electrode Electrolyte solution Electrolyte solution Electrode Electrode Sample Liquid junction Membrane

( ) E = E - E + E Measuring a potential Each link in the circuit exhibits a potential The only unknown potential is the one between the membrane and the sample, ESample The potential of the whole circuit is measured, Evoltmeter, and the unknown potential can be calculated: ( ) E = E - E + E Sample voltmeter Ref pH

pH-sensitive glass membrane Inner buffer solution with known and constant pH air bubble Ag/AgCl H+ Sample Glass membrane Constant exchange of H+ ions Varying exchange of H+ ions – dependent on sample pH The difference in potential across the glass membrane arises when there is a change in charge balance at the membrane. A difference in ion exchange on either side of the membrane occurs if the H+ concentrations (and therefore pH) on both sides are unequal. The number of positive and negative ions are no longer equal, so the potential difference across the membrane changes. In other words, the sample concentration of H+ will trigger the difference in ion exchange and cause a change in the potential across the membrane.

The amperometric measuring principle Electrodes measure the current produced during an electrochemical reaction at an electrode pO2, cGlucose, cLactate Applied voltage Ammeter - measures current Cathode - reduction Anode - oxidation Electrolyte solution - buffered Sample

pO2 and metabolite electrodes The pO2 and metabolite electrodes are designed to measure the current produced during an electrochemical reaction The flow of electrons (the current) is proportional to the concentration of the substrate (the pO2/Glu/Lac) A+ + e-  A An electrochemical reaction: - a reaction where electrons are transferred

THANK YOU