Application of pH Meters in pH Measurement of Groundwater
pH acidimeter is a common instrument mainly used for precisely measuring the acidity and alkalinity of liquid media. When fitted with corresponding ion-selective electrodes, it can also measure the millivolt (mV) potential of ion electrodes. pH meters are widely applied in environmental protection, sewage treatment, scientific research, pharmaceutical manufacturing, fermentation, chemical industry, aquaculture, tap water and other fields. This instrument is also essential testing equipment for food and drinking water plants applying for QS and HACCP certifications. Below is a brief introduction to the application method of pH meters for groundwater pH measurement. The measuring range and precision depend on the selected pH electrode and pH meter, generally accurate to 0.01 pH units.
I. Measurement Principle
pH is one of the important and frequently tested items in water analysis and a key parameter for evaluating water quality. Water pollution may cause significant changes in pH values. A high concentration of free carbon dioxide in water can markedly lower its pH value.
This method adopts a pH glass electrode as the indicator electrode and a saturated calomel electrode as the reference electrode. When immersed in the test solution, they form a primary cell. At 25℃, each pH unit corresponds to an electromotive force change of 59.1 mV. That is, every 59.1 mV change in electromotive force leads to one unit change in the pH value of the solution. After positioning calibration with standard buffer solutions, immerse the electrodes into the sample solution, and the pH value can be directly read from the pH meter. Temperature differences can be corrected by the temperature compensation device on the instrument. The color, turbidity, colloidal substances, oxidants, reducing agents and high salt content of the water sample do not interfere with the measurement. However, in strongly alkaline solutions with abundant sodium ions, errors will occur and result in low readings.
II. Required Reagents
Unless otherwise specified, the reagents used in this method are primary standard reagents or pH buffers, and the water is distilled or deionized water.
Preparation of pH standard buffer solution: Weigh the specified amount of reagent into a beaker, dissolve it in deionized water, transfer the solution into a 1000 mL volumetric flask. Adjust the temperature to 25℃, dilute with water to the mark and mix well. The deionized water used shall be boiled to remove carbon dioxide before use and cooled afterwards. Its conductivity shall be less than 2 μS/cm and pH between 5.6 and 6.0.
