Routine and reliable pH measurements
pH measurement is often a critical early step in your workflow. We offer an extensive line of pH meters, pH electrodes, pH buffers, and pH measurement accessories designed to work seamlessly together to make your complex pH measurements routine and reliable. Measure with confidence with products you trust, like Orion and ROSS electrodes.
Download the Handbook or browse through our portfolio below, or ask one of our experts to help tailor a solution specific to your needs.
What is pH and why should it be measured?
pH compares the acidity or alkalinity of a solution at a given temperature. A pH of 7 describes a neutral solution because the activities of hydrogen and hydroxide ions are equal. When the pH is below 7, the solution is described as acidic—the hydrogen ion activity increases and the pH value decreases. When the pH is above 7, the solution is described as basic (or alkaline)—the activity of hydroxide ion is greater than that of hydrogen ion.
pH electrode measurements are made by comparing the readings in a sample with the readings in standards whose pH has been defined (buffers). Thermo Scientific pH meters contain pH versus temperature values for commonly used buffers. This allows the meter to recognize a particular pH buffer and calibrate with the correct buffer value at the measured temperature.
The most common error in pH measurements
The most common cause of error in pH measurements is temperature. Temperature variations can influence pH for the following reasons:
- The electrode slope will change with variations in temperature
- Buffer and sample pH values will change with temperature
- Measurement drift can occur when the internal elements of the pH and reference electrodes are reaching thermal equilibrium after a temperature change
- When the pH electrode and temperature probe are placed into a sample that varies significantly in temperature, the measurements can drift because the temperature response of the pH electrode and temperature probe may not be similar, and the sample may not have a uniform temperature, so the pH electrode and temperature probe are responding to different environments
Electrode slope changes can be compensated for by using an automatic temperature compensation (ATC) probe or a Thermo Scientific Orion Triode electrode which has an ATC probe incorporated into the body of the electrode. Thermo Scientific pH meters calculate the electrode slope based on the measured temperature of the pH buffers. The meter will automatically adjust the pH buffer value to the actual pH of the buffer at the measured temperature.
The pH electrode should be calibrated with buffers that have known pH values at different temperatures. Since some pH meters without ATC are unable to correct sample pH values to a reference temperature, the calibration and measurements should be performed at the same temperature and sample pH values should be recorded with the sample temperature.
Anatomy of an Electrode
Discover the features of an Orion pH Electrode and how the technology works to generate accurate and reliable pH measurements.
pH measurement products & solutions
Our portfolio of benchtop and portable meters are designed to help you meet your sample analysis challenges across a wide array of industries and applications. We offer simple, complete systems that are seamlessly integrated to help address your measurement needs.
Dedicated pH testing in water, process, research and QA/QC samples. Select from simple & economical models to powerful & sophisticated meters.
Quality pH electrodes, standards and solutions are available for a variety of body materials, body styles, fill types, references styles, and functions to meet your needs.
Featured pH measurement videos
Measuring pH in drinking water using the Thermo Scientific Orion Versa Star Pro benchtop meter.
Calibrating a Thermo Scientific Orion Star A series pH benchtop meter.
Discover the Thermo Scientific Lab Star Series of Bench Meters for measuring pH, conductivity and dissolved oxygen.
Watch a pH meter calibration using the Orion Lab Star PH111 pH/mV Bench Meter.
Get to know the features of the Thermo Scientific Lab Star PH111 pH Bench Meter.
Knowledge Base: Certificates of Analysis and SDS for Orion, ROSS, AQUAfast, AquaMate, and AquaSensors products.
Orion Meters Software and Upgrades
Thermo Scientific Orion benchtop and portable meters are designed to help deliver accurate, consistent results, day after day. Boost productivity by upgrading your software today.