HUR MÄTER MAN REDOXPOTENTIALEN PRAKTISKT OCH VARFÖR BLIR DET INTE RÄTT? / How to measure the redox potential and why it often fails
The redox condition is an important factor controlling e.g. the mobility of compounds in groundwater. Reliable measurements of redox potentials in water are problematic to perform for a number of reasons. A fundamental reason is that natural waters are seldom, if ever, in a state of redox equilibrium. Each redox couple has its own potential and the measured Eh-value is a mixed potential of the individual redox couples. Only at thermodynamic equilibrium does the measured potential represent a unique redox potential for the water. Another source of error in redox measurements is the measurement technique, for example the inability of redox electrodes to respond to certain redox couples. Also, atmospheric oxygen may affect both the redox electrodes and the water, causing erroneous results. Measurements should preferably be performed in situ with a flow cell but it may rake a long time before the measured potential stabilises. To avoid some of these problems, calculations or other indirect methods could be used to estimate the redox conditions.