The pH meter is an essential piece of equipment in most laboratories, vital for many analytical and synthetic processes. Typical pH meters consist of a glass electrode connected to an electronic meter. The electrode produces a small voltage, which is converted to and displayed in pH units by the meter.
Max Cremer discovered that an electrical potential develops when two liquids of different pH levels come into contact at opposite sides of a thin glass membrane.
Fritz Haber and Zygmunt Klemensiewicz used the principle described by Cremer in 1906 to create the first glass electrode that measured hydrogen activity. However, technical difficulties, including the large internal resistance of glass electrodes, prevented the large-scale potentiometric measurements of pH. Because of these difficulties, use of a very sensitive, but expensive, galvanoscope was necessary to obtain reliable results. Today, glass electrodes are the most commonly used measuring electrodes.
Arnold Beckman proposed that the current obtained through Haber and Klemensiewicz’s electrode be amplified, allowing it to be measured using a cheap miliamperometer. He devised a simple, high-gain amplifier using two vacuum tubes for this purpose. This advance represents the development of the first pH meter, known at the time as an “acid-o-meter”.
The first commercial pH meters were introduced in the U.S. by Dr. Arnold Orville Beckman, the founder of the Beckman Instruments Company (now Beckman Coulter). The Beckman model was known as the Model G acidimeter and later renamed the Model G pH meter. This device was revolutionary because it was the first to combine the whole apparatus (amplifier, electrochemical cell, electrode, calibration dials, batteries and measuring gauge) into one unit. During its first year, Model G sales reached 444 units. The model continued to be sold until the mid-1950s, with an estimated 126,000 sold during its lifetime.
The Danish company, Radiometer, introduced its first commercially available pH meter, model PHM1. This model was an improvement on the original Beckman design, which had been found to give pH measurements that were somewhat dependent on the depth of electrode immersion.
Dr. Arthur Kuntze founded the family business, Dr. A. Kuntze, specializing in analytical instrumentation and pH meters in particular. This company is still owned by the family in its third generation.
The first laboratory combination electrode was introduced by Cannon. Improvements in sensor technology led to refinements in glass formulations that reduced alkalinity error and improved selectivity.
The first handheld pH meter was launched by NEOTEK PONSEL.
The first pH preamplifier was developed and patented by P. Carderio.
The first portable digital pH meter was designed and manufactured by Jenco Electronics in Taiwan. This meter was sold under the Cole-Parmer brand.
The porous Teflon reference junction was patented by Gary Bukamier. This replaced the earlier commonly used ceramic and wood junctions, and remains the junction of choice today.
The first single-probe portable conductivity meter was developed by Hanna Instruments.
Hanna Instruments launched the world’s first pH-controlled chemical dosing pump.
The world’s first microprocessorbased handheld pH meter was released by Hanna Instruments.
Hanna Instruments became the first company to introduce a pH electrode with a built-in temperature sensor (HI1217S). This was sold worldwide, and became ubiquitous throughout the market.
Hanna Instruments became the first manufacturer to offer an electronic, pocket-sized pH tester. Also in this year, Hanna introduced pH electronic paper (pHep®), providing for the first time a simple, accurate and affordable method of pH testing.
Hanna Instruments launched the world’s first pre-amplified pH electrode.
The first waterproof portable pH meters for use in harsh environments (HI9025) were launched by Hanna Instruments.
Hanna Instruments launched the first replaceable electrode pH pocket tester.
NEOTEK PONSEL released the world’s first pH meter with Plastogel technology.
The world’s first portable pH meter with plain-paper printing was released by Hanna Instruments.
WTW became the first manufacturer of pH meters to be certified to ISO 9001.
Denver Instruments introduced the Basic pH Meter, the first meter to feature calibration check, automatic buffer recognition and an automatic electrode efficiency test.
Denver Instruments released the Advanced AP series of portable meters. These were the first to offer a waterproof IP67 rating with “no glass” Field-Effects Transistor (FET) electrode capabilities.
Hanna Instruments became the first company to offer a pH tester with doublejunction electrode.
Denver Instruments’ 200 Series Advanced Research Meters were the first to read pH/ion/conductivity readings simultaneously.
Hanna Instruments launched the world’s first pH/temperature tester with dual level LCD.
WTW introduced several new instruments within their inoLab line that featured three function levels. These instruments set new standards for the analytical measurement of pH, oxygen, conductivity and temperature as well as for ion-selective electrodes (ISE) and multi-parameter measurements.
Hanna Instruments became the first company to offer simultaneous testing for pH and EC in a single instrument. In this year, the company also released the world’s first multi-parameter (pH/conductivity/temperature) pocket tester.
Hanna Instruments introduced the world’s first pH meter with a calibrationcheck feature.
Mettler Toledo introduced the only fully modular pH meter on the market: the SevenMulti. This pH meter offered impressive flexibility, allowing the customer to choose any combination of modules to create a tailored multichannel instrument. The instrument also allowed the customer to buy and add extra extension units at a later date, providing greater flexibility.
The first pre-amplified probe multi-parameter instrument was launched by NEOTEK PONSEL.
Hanna Instruments became the first manufacturer of process pH meters with integrated cellular communication.
The original Beckman pH meter (released in 1936) was designated an ACS National Historical Chemical Landmark in recognition of its significance as the first commercially successful electronic pH meter.
The Docu-pH from Sartorius Mechatronics featured DocuClip® for sensor identification. DocuClip® technology was the first to provide complete documentation to ISO/ GLP/GMP and 21 CFR Part 11 FDA standards on electronic records.
Hannah Instruments launched the world’s first pre-amplified probe multi-parameter portable meter.
SCHOTT Instruments introduced the first pH meters with integrated PC capability— the ProLab 3000 and ProLab 4000—offering Windows-comparable menu structure and mouse handling.
Denver Instruments released the Meridian pH Meter with GLP clip technology, to meet ISO/GLP/GMP and 21 CFR Part 11 FDA standards on electronic records.
Metrohm US launched the Metrohm 827 pH Lab, a versatile, GLP-compliant pH measurement system. This instrument offered the new Primatrode™ combination electrode with an integrated temperature probe, a measuring resolution of pH 0.001, automatic buffer recognition and temperature compensation.
Metrohm launched the 867 pH Module, equipped with both conventional and intelligent measurement inputs for pH, potential, ion and temperature measurements. An integrated electrode test was able to quickly check the electrode and deliver troubleshooting information.
Hach Lange launched the pH ultra, which offered rapid measurement for all sample types, even difficult samples such as low-ionic strength (pure) water.
NEOTEK PONSEL manufactured the world’s first pH/T digital sensor with pH cartridge.
SCHOTT launched the IoLine electrode with an iodine/iodide reference system in place of the traditional Ag/AgCl reference system for the most demanding laboratory measurements. The patented 3-chamber system with iodine reservoir in the reference electrode offered an increased working life, while the lower temperature dependence of the iodine/iodide reference potential allowed greater accuracy of measurements at changing temperatures or at a temperature that differs from the calibration temperature.
The Future For pH Meters
Like many laboratory instruments, pH meters have evolved beyond all recognition over the last several decades. However, experts predict a gradual evolution rather than a revolution in the design of pH meters during the coming years. It seems likely that the product hardware will continue its trend towards miniaturization, while software will undoubtedly become easier to develop and use. Although its form and function may change little in the immediate future, it seems certain that the pH meter will continue to enjoy its status as one of the most ubiquitous pieces of laboratory equipment.