Biotech-Lab User Manual
\\
25
www.ibpmedical.com
Three possible calibration results.
7.5.2 BACKGROUND OF PH MEASUREMENT
For measuring pH, a combined electrode is used. Combination pH electrodes are combinations of one reference
electrode and one measuring electrode in a glass tube. The pH value in the dialysate is measured by an
unbreakable pH-electrode. The glass body is protected with a plastic coat and due to the jelly-electrolyte-filling, it is
maintenance-free. This electrode’s diaphragm must be stored in 3 mol/l KCl-solution. The protective cap must be
refilled every three to four weeks to prevent the electrode from drying out. Before use the electrode must be
checked for exterior damage and crushed glass. Crusts caused by leaking electrolyte can be removed easily by
rinsing with reverse osmosis-treated water.
The sample volume should be 100 ml of dialysate or 1 liter of untreated water. The sample should be poured into a
clean glass container with a tube or hose, coming into as little contact with air as possible. The pH-value must be
measured immediately in the same container. Make sure that the display stabilizes before the value is read. In
stirred solutions the response rate is faster; the value, however, must be measured at resting fluid.
The pH-electrode must be dabbed only with a lint-free cloth and never rubbed dry. Rubbing destroys the jelly layer
on the glass surface which results in a longer response time for the electrode.
Pressure and fluid currents have considerable influence on the pH measurements. For high accuracy pH
measurement it is essential to take the pH measurement in a resting solution at environmental pressure.
