PH meter

Summary

A pH meter is a scientific instrument that measures the hydrogen-ion activity in water-based solutions, indicating its acidity or alkalinity expressed as pH. The pH meter measures the difference in electrical potential between a pH electrode and a reference electrode, and so the pH meter is sometimes referred to as a "potentiometric pH meter". The difference in electrical potential relates to the acidity or pH of the solution. Testing of pH via pH meters (pH-metry) is used in many applications ranging from laboratory experimentation to quality control. The rate and outcome of chemical reactions taking place in water often depends on the acidity of the water, and it is therefore useful to know the acidity of the water, typically measured by means of a pH meter. Knowledge of pH is useful or critical in many situations, including chemical laboratory analyses. pH meters are used for soil measurements in agriculture, water quality for municipal water supplies, swimming pools, environmental remediation; brewing of wine or beer; manufacturing, healthcare and clinical applications such as blood chemistry; and many other applications. Advances in the instrumentation and in detection have expanded the number of applications in which pH measurements can be conducted. The devices have been miniaturized, enabling direct measurement of pH inside of living cells. In addition to measuring the pH of liquids, specially designed electrodes are available to measure the pH of semi-solid substances, such as foods. These have tips suitable for piercing semi-solids, have electrode materials compatible with ingredients in food, and are resistant to clogging. Potentiometric pH meters measure the voltage between two electrodes and display the result converted into the corresponding pH value. They comprise a simple electronic amplifier and a pair of electrodes, or alternatively a combination electrode, and some form of display calibrated in pH units. It usually has a glass electrode and a reference electrode, or a combination electrode.

Official source

https://en.wikipedia.org/wiki/PH_meter

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Enhanced in situ bioremediation of chlorinated solvents is, especially in source zone remediation, often limited through the accompanied high acidification of groundwater. This acid built-up originating from the dechlorination itself and fermentation products, such as organic acids, presents a draw-back in the efficiency of dehalorespiring bacteria. It is therefore indispensable to develop and implement appropriate buffering strategies to ensure a constant transformation of toxic chloroethenes to the final non-toxic product ethene. In this study pH tolerance of different dehalorespiring bacteria was tested. The limiting acidic pH varies significantly among the consortia. The consortium SL23b4 (PCE to ethene) grows at all the examined pH (pH 5 to pH 7.5) with a pH optimum between 6 and 7 (depending on the dechlorination step), whereas Maroc 6b (PCE to ethene) was only found to grow at incubation pH of 7, and very slowly at pH 6.5. The consortium 2SO (cis-DCE to ethene) seems to be inhibited at acidic pH (no growth at pH 5 and 5.5) having a pH optimum above neutral pH. In most cases incomplete dechlorination was observed in cultures growing at acidic pH or below the pH optima, accumulating toxic intermediate dechlorination products as a consequence. Additionally, high rates of dechlorination were always accompanied by pH drops up to 1.2 pH units, giving evidence of high acid production. pH had also influence on the community composition. In the consortium SL23b4 a shift from a Dehalococcoides- (pH 6-7.5) to a Sulfurospirillum spp.- (pH5 -5.5) dominated community was observed. Consortium Maroc 6b showed significantly different community compositions due to a pH change of only 0.5 pH units. Dehalococcoides spp. and Dehalobacter spp. were dominating at pH 7 and pH 6.5, respectively. Consortium 2SO is dominated by Dehalococcoides spp. at all pH, although at pH 7 a much higher diversity seems to prevail, with the threefold number of OTUs. Tests on the tolerance of the dehalorespiring consortia for elevated PCE concentration showed similar patterns for the different dechlorination steps, as for pH cultures, and confirmed a generally higher sensitivity towards PCE and pH changes for the last steps of dechlorination. Conclusively, Dehalococcoides spp., the only known genera able to perform complete dechlorination, seem to be highly sensitive to pH and PCE changes. Further, abiotic experiments on silicate mineral dissolution, using forsteritic olivine, were performed to simulate the buffer capacity of the minerals for the acid production during microbial reductive dechlorination. In these experiments, the buffer capacity was insufficient to counterbalance the constant acid titration rate, resulting in a final pH between 3 and 4 (initial pH of 7). The formation of precipitates, such as iron oxide, and the re-precipitation of magnesium were observed in some cases, showing a decrease in magnesium concentrations.

2010

pH control in small scale shaken bioreactors

EPFL2002

2010