pH meters
Quality pH-meters by Mettler-Toledo are available in the Analytics-Shop.
These are used in many different areas. For instance, in industries which require very precise measurement results to maintain hygiene standards, like in the food and beverage industry and fulfilling requirements in wastewater treatments and water purification methods.
pH measurement with glass electrodes
pH meters with glass electrodes are the most commonly used measuring devices. Hence, this electrode is generally known as the "pH-electrode". In this method, the electric potential of the glass electrode is measured which is directly dependent on the H+ ion concentration. The potential difference to the reference electrode resulting from the voltage difference converts into the pH reading. The reference electrode is normally a silver-silver chloride half cell which is joined together with the pH electrode to form a combination electrode
Advantages:
- most common method of pH measurement
Disadvantages:
- only slightly more resilient electric current can be generated, i.d. interference of the measurement by the flow potential is easily possible
- both the zero indicator and the increase must be adjusted before calibration
- the diaphragm may be contaminated or worn out
pH measurement with field effect transistors
This involves using pH meters with ion-sensitive field effect transistors (ISFET).
Advantages:
- pH values are more stable
- add on electronics unit show more consistent results
Disadvantages:
- less number of possible measurement processes (= lifetime)
- relatively unpopular type of pH measurement
pH measurement with hydrogen electrodes
Traditional method of pH measurement with the use of hydrogen electrodes. This technique is based on the pH dependence of the hydrogen potential.
Advantages:
- high mechanical stability
- input resistance (impedance) is very low
- no alkali error
- no acid error
Disadvantages:
- exhibit sensitivity to heavy metal salts (copper, silver, mercury)