The pH meter is referred to as the acidity meter, which is mainly composed of two parts: the electrode and the electric meter. The electrode part usually contains a reference electrode, a glass electrode, and a galvanometer to achieve pH measurement. THE OPERATING PRINCIPLE IS BASED ON THE POTENTIAL DIFFERENCE GENERATED BY THE GLASS ELECTRODE FOR SOLUTIONS WITH DIFFERENT HYDROGEN ION CONCENTRATIONS, WHICH IS CONVERTED INTO AN INTUITIVE PH VALUE DISPLAY BY THE ELECTROMETER. This measurement method is accurate and efficient, but requires high operating specifications.
ENABLE THE PH METER CORRECTLY
When it comes to properly enabling the PH meter, there are many things that need to work together. First of all, it is necessary to accurately confirm the use of the power supply, strictly ensure that the power supply voltage of the use environment is consistent with the frequency and the data marked on the nameplate of the instrument, and the grounding must be good, otherwise the digital display is very likely to be unstable or the pointer shakes during the measurement. When the instrument assembly is connected and assembled, the bakelite cap of the glass electrode is firmly clamped to the small clamp of the electrode clamp, and the metal cap of the calomel electrode is clamped to the large clamp, and the height of the two electrodes is flexibly adjusted with the help of the electrode clamp head screw. FOR THE USE OF PH ELECTRODES, THE GLASS ELECTRODE MUST BE SOAKED IN DISTILLED WATER FOR MORE THAN 24 HOURS BEFORE INITIAL USE, AND THE CALOMEL ELECTRODE MUST BE SOAKED IN SATURATED POTASSIUM CHLORIDE SOLUTION BEFORE INITIAL USE, AND CANNOT BE IMMERSED IN DISTILLED WATER WITH THE GLASS ELECTRODE.
PREPARE THE PHMETER STANDARD BUFFER CORRECTLY
Preparation method:
For the standard buffer of PH=4.00, 5.07 grams of potassium hydrogen phthalate dried at 105 °C for 1 hour were accurately weighed, and the volume was fully dissolved after adding re-distilled water, and the volume was set to 500 ml. THIS BUFFER IS COMMONLY USED TO CALIBRATE PHMETER MEASUREMENTS IN THE ACIDIC RANGE.
For the standard buffer pH = 6.88, you can choose to weigh 3.401 g of potassium dibasic phosphate dried at 130 °C for 2 hours, or 3.549 g of anhydrous dibasic sodium phosphate, and dissolve in distilled water with the same weight and make a volume of 500 ml. THE BUFFER IS IN THE NEUTRAL RANGE AND PLAYS AN IMPORTANT POSITIONING ROLE IN THE CALIBRATION OF THE PH METER.
PH=9.18 standard buffer, weigh 3.8144 grams of sodium borate, dissolve in distilled water and set the volume to 100 ml. Suitable for calibration in the alkaline range.
How to save it
The preservation of standard buffers is critical to their stability and accuracy. The PH reference material should be stored in a dry environment, such as mixed phosphate PH reference material, once the air humidity is high, it is easy to deliquescent, and the deliquescent reference material will lose its calibration value due to the change of composition. When preparing standard solutions, it is recommended to use secondary distilled water or deionized water, and if it is only used for 0.1 grade pH meter measurements, ordinary distilled water can also meet the requirements. Dilution with a smaller beaker reduces the residue of the solution on the walls of the cup. The container where the reference material is stored should not only be poured to remove the residue, but also rinsed with distilled water several times before pouring the prepared solution to ensure that the solution concentration is accurate. In general, the prepared standard buffer solution can be stored for 2-3 months, and should be discontinued immediately if it is turbid, moldy or sedimentate. For alkaline standard solutions, they need to be stored tightly sealed in polyethylene bottles to prevent carbon dioxide from intruding to form carbonic acid, resulting in a decrease in pH.
calibration
ALTHOUGH THERE ARE MANY TYPES OF PH METERS, MOST OF THEM USE THE TWO-POINT CALIBRATION METHOD. First, the electrometer was positioned with a standard buffer of PH=7, and then according to the acidity and alkalinity of the solution to be measured, the buffer with pH=4 for acidity and PH=9 for alkalinity was selected. THE MANUAL PH METER NEEDS TO BE ADJUSTED BACK AND FORTH BETWEEN THE TWO BUFFERS UNTIL THE ZERO POINT AND THE POSITIONING KNOB NO LONGER NEED TO BE MOVED AND THE BUFFER PH VALUE CAN BE ACCURATELY DISPLAYED. THE SMART PH METER AUTOMATICALLY RECOGNIZES THE CALIBRATION, BUT TO ENSURE THAT THE STANDARD BUFFER IS SELECTED AND PREPARED CORRECTLY, PAY ATTENTION TO THE TEMPERATURE OF THE TEST SOLUTION AND ADJUST THE TEMPERATURE COMPENSATION KNOB BEFORE CALIBRATION. Generally, the frequently used PH meter does not need to be calibrated again within 48 hours, but if there is a large difference in the temperature of the solution, the electrode is exposed for more than 0.5 hours, the adjustment knob is mismoved, the strong acid and alkali solution is measured, the electrode is changed, and the measured PH value deviates from the calibration range, etc., it must be recalibrated.
Precautions
Composite electrodes commonly used in laboratories are easy to use, interference-resistant, and fast to balance. When in use, remove the electrode dosing port and the lower end rubber sleeve to maintain the hydraulic difference. When not in use, soak in 3mol/L potassium chloride solution, avoid using washing liquid or absorbent reagent. Check the glass electrode bulb before use, it should be transparent without cracks and bubbles, and if there are bubbles, they can be shaken off lightly, and the bulb should be replaced if it is broken. The time should be shortened for measuring the high concentration solution, wash it after the measurement, and blot the glass membrane with filter paper. During the measurement, the solution should be prevented from seeping into the replenishment hole, otherwise the display will jump randomly. The electrode should not be used for strong acids and alkalis, corrosive solutions and dehydrated media.
IN CONCLUSION, PH METERS PLAY A CRUCIAL ROLE IN SCIENTIFIC RESEARCH, INDUSTRIAL PRODUCTION, AND MANY OTHER FIELDS WHERE PRECISE PH measurement is required. PROPER ACTIVATION OF THE PH METER, FROM POWER SUPPLY CONFIRMATION, COMPONENT CONNECTION ASSEMBLY, TO ELECTRODE ACTIVATION, IS THE FOUNDATION FOR THE ACCURACY OF SUBSEQUENT MEASUREMENTS. PROPER PREPARATION AND STORAGE OF STANDARD BUFFERS, AS WELL AS PRECISE CALIBRATION ACCORDING TO THE CHARACTERISTICS OF DIFFERENT TYPES OF PHMETERS, ARE KEY TO ENSURING RELIABLE MEASUREMENT RESULTS. THE CORRECT OPERATION AND DAILY MAINTENANCE OF THE PHMETER ELECTRODE DURING USE CAN EFFECTIVELY EXTEND THE SERVICE LIFE OF THE ELECTRODE AND FURTHER IMPROVE THE MEASUREMENT ACCURACY. Only by mastering and strictly implementing these key points about the use and maintenance of PH meters can we give full play to the performance advantages of PH meters, provide solid support for the accurate acquisition of experimental data and precise control of the production process, and help the efficient and stable development of various industries.
