Sensors and electrodes

Measurement of pH is one of the basic activities that the lab technician performs in the laboratory.pH is the so-called quantitative scale of acidity and alkalinity of aqueous solutions of chemical compounds. The pH scale is based on measuring the activity of hydrogen ions in aqueous solutions.The pH of solutions is comparative and is a dimensionless unit. The vast majority of pH meters are potential meters, in which the pH value is determined by measuring the electromotive force (SEM) of the cell, which is formed from an indicator electrode immersed in the test solution and a comparison electrode that is immersed in a standard solution of known pH. The electrode immersed in the test solution and the electrode immersed in a solution of known properties are usually connected by a sensitive and accurate voltmeter, which automatically converts the measured electromotive force of the cell so formed into a pH scale. In some electrodes, the reference semi-cell is enclosed in a special cartridge that acts as a barrier to silver ions. The indicator element of the pH electrode is a membrane made of glass with a specially selected composition. The pH sensors and electrodes that are used in practice can be operated for a long period of time, as it is possible to refill them with electrolyte. The possibility of refilling with electrolyte significantly reduces the cost of use. During normal use of pH sensors and electrodes, the overpressure inside causes the electrolyte to gradually flow out, which is why it is necessary to refill it after some time. Electrodes can be made, either as half-cells or as combination electrodes (measuring cells). The use of half-cells requires the use of a separate reference electrode.There are many pH sensors and electrodes on the market, but special attention should be paid to several important aspects. First, we should choose a particular sensor or electrode for the solution in which we want to determine the pH. We will choose a different sensor (electrode) for very liquid solutions, and another for viscous and dense substances. The measurement characteristics themselves are also extremely important - whether we are measuring a "standing" solution or whether we will need to measure in a current or mixed solution. Measurement accuracy is another very important element that determines the work of the laboratory technician and is directly related to the chosen sensor and electrode. Sometimes, for very simple measurements, you can choose so-called testers that permanently have the electrode bound to the microprocessor chip and do not allow for electrolyte replenishment, these are "disposable" devices. Selection of the right pH sensor and electrode is extremely important, sometimes it is the first step to properly performed further activities of the laboratory technician, pH can have an insanely significant impact on the course of the technological process, and its fluctuations even in the range of tenths of a pH can affect the success or failure of a given process.