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Published in Frank R. Spellman, Fundamentals of Wastewater-Based Epidemiology, 2021
A pH meter measures the electric potential (millivolts) across an electrode when immersed in water. This electric potential is a function of the hydrogen ion activity in the sample; therefore, pH meters can display results in either millivolts (mV) or pH units. A pH meter consists of a potentiometer, which measures electric potential where it meets the water sample; a reference electrode, which provides a constant electric potential; and a temperature compensating device, which adjusts the readings according to the temperature of the sample (since pH varies with temperature). The reference and glass electrodes are frequently combined into a single probe called a combination electrode. A wide variety of meters are available, but the most important part of the pH meter is the electrode. Thus, purchasing a good, reliable electrode and following the manufacturer’s instructions for proper maintenance is important. Infrequently used or improperly maintained electrodes are subject to corrosion, which makes them highly inaccurate.
Air Sampling
Published in Martin B., S.Z., of Industrial Hygiene, 2018
Potentiometric sensors are instruments that use a change in electrochemical potential as their principle of detection and are most commonly represented by the pH meter. Potentiometry is strictly defined as the measurement of the difference in potential between two electrodes in an electrochemical cell under the condition of zero current. Gases and vapors can react with reagents, resulting a redox reaction, the extent of which is proportional to the concentration of the reacting gas. Whereas potentiometry is basically a nonspecific technique, some degree of specificity may be obtained through the selection of the membrane through which the gaseous analyte must diffuse to enter the electrochemical cell, the selection of the reagent, and the type of electrodes used. Potentiometric instruments are used for the measurement of a variety of contaminants, including carbon monoxide, chlorine, formaldehyde, hydrogen sulfide, nitrogen oxides, oxygen, ozone, and sulfur oxides.
Electrochemical Composition Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Michael J. Schöning, Arshak Poghossian, Olaf Glück, Marion Thust
Electrochemical analysis in liquid solutions is concerned with the measurement of electrical quantities, such as potential, current, and charge, to gain information about the composition of the solution and the reaction kinetics of its components. The main techniques are based on the quantitative determination of reagents needed to complete a reaction or the reaction products themselves. Four traditional methods of electrochemistry are described here (Figure 55.1): potentiometry, voltammetry, coulometry, and conductometry. Potentiometry implies the measurement of an electrode potential in a system in which the electrode and the solution are in electrochemical equilibrium. Voltammetry is a technique in which the potential is controlled according to some prescribed function while the current is measured. Coulometry involves the measurement of charge needed to completely convert an analyte, and conductometry determines the electrical conductivity of the investigated test solution. The practical applications of these measurement techniques for analytical purposes range from industrial process control and environmental monitoring to food analysis and biomedical diagnostics. The analytical methods and their instrumentation as well as recent trends, such as electrochemical sensors, are discussed.
Review of pH sensing materials from macro- to nano-scale: Recent developments and examples of seawater applications
Published in Critical Reviews in Environmental Science and Technology, 2022
Roberto Avolio, Anita Grozdanov, Maurizio Avella, John Barton, Mariacristina Cocca, Francesca De Falco, Aleksandar T. Dimitrov, Maria Emanuela Errico, Pablo Fanjul-Bolado, Gennaro Gentile, Perica Paunovic, Alberto Ribotti, Paolo Magni
Potentiometric sensors are the most used for routine pH determination. In principle, a potentiometric measurement consists of the measurement of the electromotive force (EMF) in an electrochemical cell, composed of a working electrode and a reference electrode. The pH of the sample is calculated comparing the EMF measured in the sample (Es) and in a standard buffer solution (Eb) of known pH (pHb), following the Nernst equation: where R is the gas constant, F is the Faraday constant and T is the temperature (Rérolle et al., 2012).