pH meters

In the Analytics-Shop you will find - among others – the quality pH-meters by Mettler-Toledo.

These are used in many different areas. For instance in applications that require very accurate measurement results, particularly in the area of hygiene (food and beverage) they play an important role or even in demanding wastewater applications and pure and ultrapure water.

pH measurement with glass electrodes

pH meter with glass electrodes are the most commonly used measuring devices, therefore the said electrode is generally referred to as "pH-electrode". In this method the electric potential of the glass electrode is used which is directly dependent on the H+ ion concentration. Consequently the potential difference to the reference electrode resulting from the voltage reflects the pH level substantially linear. The so-called "reference electrode" is a silver-silver chloride half cell in most cases which is joined together with the pH electrode to a rod measuring chain

Advantages:

• widespread method of pH level measurement

Disadvantages:

• only slightly more resilient power can be generated, i.d. interference of the measurement by the flow potential is easily possible
• calibration of both the zero point and the gain/ increase must be adjustable
• the diaphragm can be contaminated or drained

pH measurement with field effect transistors

The second option is using pH meters with ion-sensitive field effect transistors (ISFET).

Advantages:

• the pH values are more stable
• retrofitted electronics show resistancy and sturdiness

Disadvantages:

• number of possible measurement processes (= lifetime) is less
• relatively unpopular type of pH measurement

pH measurement with hydrogen electrodes

Last but not least some more information about a traditional method of pH measurement: 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)