The pH Tester, Meter, and Other pH Instruments

pH is a measure of a liquid’s acidity or alkalinity, via a pH tester, meter, or other pH indicator, according to the relative quantity of hydrogen ions (H+) in the liquid. The greater the concentration of H+ ions in the liquid, the more acidic the solution is and the lower the pH. Conversely, the lower the H+ concentration, the more basic (or alkaline) the solution is and the higher the pH.

pH is formally defined as the negative log of H+ activity. This means that every pH unit expresses a tenfold change in acidic strength.

pH measurement is critical to a variety of industries such as water and wastewater treatment, chemical production, agriculture, environmental monitoring, life science research, pharmaceutical production, and electronics manufacturing. Consequently, pH is now the most widely tested chemical parameter in the world.

Measuring pH

pH can be quickly measured with litmus paper or pH indicators. These are convenient because of their low cost and ease of use, but they can only provide a rough indication of pH, which is insufficient for most applications. The more accurate method involves the use of a measurement system consisting of a pH meter, an electrode that is sensitive to H+ ions, and calibration buffer solutions. The effect that H+ ions have on the electrode can be measured and converted to a pH value by the meter.

Choosing a pH Measurement Instrument

Pocket-sized testers are known for their low cost and small size. Handheld, portable meters typically offer more features than testers and are good for laboratory and field use. Benchtop meters are ideal for stationary lab applications typically offering larger displays and more robust data management than other types of meters. ISFET (ion-specific field effect transistor) meters are a unique subset of pH meter that utilize a silicon chip sensor in lieu of a traditional pH-sensitive glass bulb electrodes. This makes them perfect for applications where the presence of glass presents an issue such as with food production.

Electrode and Buffers

Most pH measurement systems feature standard pH electrodes with glass bulbs made from pH-sensitive glass, yet there is a wide variety of configurations to handle specialized applications.

All pH meters require calibration standards to ensure that the readings are traceable to a standard. Always choose a pH 7 buffer plus at least one other pH value close to your expected measurement range. Using solutions of known pH value allow you to adjust the system to read accurate measurements. Calibration should be performed before each set of readings.

See a selection of pH measurement instruments.