Industrial pH Sensor Fundamentals
The Electrode Used for Measuring A measurement electrode that is specifically made for this purpose can be used to determine the pH sensor measurement of an aqueous solution.
The platinum/hydrogen electrode has been used to measure the concentration of hydrogen ions in aqueous solutions since its creation in 1897. It still serves as a reference standard for the electrometric measurement of pH in addition to carrying out this job today. The platinum plate or rod that serves as the hydrogen electrode is platinized, coated in platinum black, and passed through a stream of hydrogen gas. The silver wire that makes up the reference electrode has been treated with silver chloride. The main concept that guides the use of a hydrogen electrode is as follows: A metal rod can get ionized when it is immersed in an aqueous solution that includes its own salt, which results in the ionization of the atoms on its surface. A silver electrode, for instance, may get ionized when immersed in silver nitrate. The rod’s metal will acquire a negative charge as a result of the positively charged metal ions on its surface being pulled to the negatively charged water molecules. A potential difference is produced as a result of this charge exchange at the phase transition between metal and solution. The potential sometimes referred to as the galvanic potential, varies according to the number of ions present in the solution. The hydrogen electrode is still employed as a reference standard in modern times, in part because the results of its measurements are so exact. The hydrogen electrode, on the other hand, has lost its significance due to its difficulty in handling for a variety of more pragmatic reasons. The antimony electrode is the only one that has survived out of all the other metal electrodes. The acid frequently used to etch glass, hydrofluoric acid, has no effect on antimony. However, both the measuring range and the precision are severely constrained. Antimony should be treated carefully because it is a chemical that has been linked to human cancer.
Glass is used for the electrode. pH sensor measurement wasn’t made into an easy-to-use, reliable tool that could be applied in a variety of situations until the glass electrode was developed. In recent years, glass electrodes have outperformed all other types of indicator electrodes for pH measurements, becoming the preeminent type of electrode utilized for these studies. The pH sensor measurement of an aqueous solution is now as commonplace as the measurement of temperature and pressure because of the dependability and accuracy of the glass electrode combined with exceptionally steady electronic amplification. You will learn all you need to know in this book on the glass electrode’s operation and upkeep, enabling you to successfully use it. The shaft of a glass electrode is made of glass; this shaft must have a robust resistance to hot alkaline solutions and an electrical resistance that is many times greater than that of the membrane glass. An electrode made of glass has glass for the shaft. The part of the glass electrode that is pH-sensitive is the electrode tip, sometimes referred to as the glass membrane. It has a hemispherical shape.
The membrane is attached to the electrode shaft by a special glass that is sensitive to hydrogen ions. The pH sensor Cable buffer solution, which normally has a pH sensor value of 7, is partially saturating the glass electrode.
A specified amount of potassium chloride, or KCl, is added to this internal buffer. A silver wire coated with silver chloride (Ag/AgCl) and inserted through the glass electrode all the way down into the internal buffer serves as a conducting electrode. A circuit for electrochemistry is therefore created. Using the coaxial pH cable’s core, a connection has been created between the Ag/AgCl wire and one of the terminals on a pH sensor meter. Glass is used for the Membrane. All types of glasses produce a potential difference in relation to the hydrogen ion concentration in aqueous solutions as a common characteristic. The typical McInnes glass (Corning 015) is one variety that can provide galvanic potentials that are consistent with the NERNST equation over a wide pH range.
A thin gel layer of about 10-4 mm thickness is created between the glass surface of the membrane glass of a measuring electrode and the aqueous solution when the two come into contact. The solution cannot pass through this gel layer, which serves as a barrier. The thickness of the gel layer is influenced by the quality and composition of the membrane glass, as well as the temperature and pH level of the test solution. The internal side of the glass membrane contacting the inner buffer, an aqueous solution with a pH of 7, causes a gel layer to form on the inside of the glass membrane as well. The gel layers and the H+ ions that are present in the solutions are constantly exchanging H+ ions on both sides of the membrane. The outcome of this ion exchange depends on how many H+ ions are present in either or both solutions. When equilibrium is reached between the hydrogen ions in the solutions and the hydrogen ions in the gel layers, assuming that the concentration of hydrogen ions in each solution is the same on both sides of the glass membrane, the ion exchange will stop. Even if the hydrogen ion concentration in each solution is the same on both sides of the glass membrane, this is still the case. As a result, there is no difference in potential between the two sides of the membrane glass, which means that both sides have the same potential.
There may be a discrepancy between the inner and outer sides of the membrane glass if the concentration of hydrogen ions varies between the inner buffer and the outer solution. According to the pH difference between the inner buffer and the outer solution, the size of this potential difference will vary. To be able to gauge the membrane’s potential, the membrane must possess some degree of conductivity on its own. This is made feasible by the alkaline ions in membrane glasses being mobile (most modern membrane glasses have Li+ ions, whereas previous membrane glasses had Na+ ions). The thickness of the gel layer and the makeup of the gel both have an impact on the reaction time and the glass electrode’s distinctive slope. The gel layer is therefore of utmost importance to the electrode’s overall effectiveness.
Without the gel layer, a pH sensor measurement is not possible. Unfortunately, it takes a gel layer between one and two days to fully develop. In order to avoid this, a measurement electrode must be hydrated (immersed in ordinary, clean tap water) for at least twenty-four hours before usage. Most manufacturers ship their electrodes with the membrane already hydrated (the membrane is kept moist with a KCl solution that is enclosed beneath a plastic cap), making the electrode instantly usable.
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