Intro to pH and ORP

For the non-scientist or engineer, pH and ORP are the most well known analytical measurements. People often get their first experience measuring the pH of acids and bases by using litmus paper in school chemistry classes. Later they may hear references to oxidation with household cleaners or even the paint fading on their automobile.

The articles listed below are compiled from common questions Hamilton has received from our users. They cover topics from basic sensor functionality to questions about the installation, usage, calibration, and care of pH and ORP probes, and pH buffer solutions. We hope you will find them useful in your daily work with these measurements.

pH Basics

Ever wonder how pH sensors actually work? This video goes through the basic design and functionality of the standard glass membrane combination pH sensor.

Topics Within the Video:

• What is pH actually measuring?
• The relationship with hydrogen ion concentration and millivolt output of the sensor.
• Measurement electrode versus reference electrode.
• Zero point (offset) and slope values.
• What are the effects of temperature on pH measurement?

pH Articles

Principles of pH

pH has become a unit of measure so commonplace that it is now even referred to in consumer household products such as cosmetics, shampoo, and even food / beverage. It is important to ask - what are we actually measuring when we refer to pH?

pH Sensor Design

The first commercially available glass membrane pH sensors were launched to the marketplace in the mid-1930s. The sensors of today still rely on the same design principles as these first products.

pH Probe Operation Principles

The standard output signal of a glass membrane pH probe is voltage. This series of articles looks at the terminology used to define the voltage. It reviews concepts such as slope, offset, asymmetry, and the isopotential point.

Sources of pH Measurement Error

pH Sensors are electrochemical devices with limited lifespans. Changing process conditions directly impact each component within the combination electrode thus can be sources of error leading to inaccuracy and eventual death of the sensor.

pH Calibration

The ever-changing nature of the electrochemical pH measurement requires that periodic calibration of the sensor is performed. The topic of calibration inevitably creates questions about the frequency and the procedure required to ensure the accuracy of the pH measurement.

Care and Maintenance

The best way to maximize lifespan of process pH sensors is proper storage and cleaning. The pH sensitive gel layer that forms on the glass membrane must be kept hydrated for proper measurement and response time.

pH Probe Accessories

The articles below tackle the most essential pH probe accessories - calibration buffers and interconnection cabling.

pH and ORP Sensor Installation Tips

This brief article describes some common considerations with sensor installation and removal, as well as best practices for mounting.

pH and ORP Sensor Cleaning

Answers to common questions on how to clean off build-up and coating on pH sensors and ORP sensors.

pH Glass Membrane Types

Hamilton offers several different options for pH membrane glass. This article describes the purpose of each glass type.

pH and ORP Sensor Reference Design

Pre-Pressurized vs. refillable vs. polymer vs. viscous electrolyte? This article discusses basic pH reference design benefits for each product family.

pH / ORP Sensor Storage and Regeneration

How to store a pH sensor? How long can the sensor sit dry? How can the sensor be regenerated? Learn more in this article.

pH Sensor Shelf Life and Expiration

This article discusses common questions about pH sensor shelf life and pH sensor expiration.

pH Drift From Autoclavation or SIP

This technical article dives into why pH sensor may exhibit drift after autoclave or SIP cycles and glass membranes that limit drift.

What is a Liquid Earth (LEVP) for a pH sensor?

Some Hamilton process pH sensors have the option for a liquid earth (LEVP) connection; however many end-users are unfamiliar with its benefits.

Temperature Influence on DuraCal pH Buffers

Temperature has a direct effect on the pH of liquid buffer solutions. This page provides one easy place to see the temperature effects on all Hamilton pH buffers.

Connecting Arc pH / ORP Sensors to the Bioreactor

There are several methods for connecting Arc pH and ORP sensors to the bioreactor. This article explores your options.

Stability and Accuracy of DuraCal pH Buffers

Questions often come up regarding pH buffers, their stability (shelf life), and impact on accuracy. This knowledgebase article takes on many of these topics.

Tips to Improve pH Measurement

Accurate pH control is fundamental for a wide variety of industrial bioprocesses. Some of those processes are based on cell or microbial cultures where the pH value has to be kept within a narrow range. This video shows the three most helpful tips to ensure optimal growth and product yield.

Comparing Glass Membrane Versus Optical pH Sensors

In biopharma applications there are two technology options for continuous pH measurement - glass membrane and optical. This article will explore both technologies along with their benefits and limitations.

pH Basics Video

Ever wonder how pH sensors work? This video discusses basic design and functionality of glass membrane combination pH sensors.
ORP probes

ORP Basics

ORP is an abbreviation for “Oxidation Reduction Potential” and is commonly referred to as a “Redox” as the sensor is used to measure redox reactions.


• How Do ORP Sensors Work?
• What is the ORP unit of Measure?
• What effect does temperature have on ORP?
• What effect does pH have on ORP?


ORP Articles

pH measurement guide cover

Download Our pH Measurement Guide

Get a better understanding of pH measurement in Hamilton’s comprehensive pH Measurement Guide.