The acidity meter is a commonly used instrument and equipment. It is mainly used to accurately measure the pH value of liquid medium. It can also measure the MV value of ion electrode potential with the corresponding ion selective electrode. It is widely used in industrial, agricultural, scientific research, environmental protection and other fields. Plant Extract,Pine Pollen Powder,Natural Food Coloring,Ginkgo Biloba Extract Powder Youth Biotech CO,. Ltd. , https://www.youtherb.com
The narrowly defined acidity meter mainly refers to the laboratory acidity meter, which is mainly divided into three categories: benchtop acidity meter, portable acidity meter and pen type acidity meter.
First, the principle of acidity meter
Potentiometric measurement with a pH meter is the most sophisticated method of measuring pH. The pH meter consists of three parts:
1 a reference electrode;
2 a glass electrode whose potential depends on the pH of the surrounding solution;
3 An galvanometer that measures a small potential difference in a circuit with a very high resistance. Thanks to the latest electrode design and solid-state circuit technology, the best pH now distinguishes 0.005 pH units. The basic function of the reference electrode is to maintain a constant potential as a measure of various off-potentials. The silver-silver oxide electrode is currently the most commonly used reference electrode in pH. The function of the glass electrode is to establish a potential difference that reacts to changes in the hydrogen ion activity of the measured solution. Putting the pH sensitive electrode and the reference electrode in the same solution, a galvanic cell is formed, the potential of which is the algebraic sum of the potential of the glass electrode and the reference electrode. E battery = E reference + E glass, if the temperature is constant, the potential of this battery changes with the pH of the solution to be tested, and measuring the potential generated by the battery in the pH meter is difficult because its electromotive force is very small, and the circuit The impedance is very large 1-100 MΩ; therefore, the signal must be amplified to make it sufficient to drive a standard millivoltmeter or milliampere meter. The function of the galvanometer is to amplify the potential of the primary battery several times. The amplified signal is displayed by the electric meter. The degree of deflection of the meter pointer indicates the strength of the signal it pushes. For the purpose of use, the dial of the pH ammeter is engraved accordingly. The pH value; while the digital pH meter directly displays the pH numerically.
Second, the acidity meter debugging
The pH meter commonly used in laboratories is the old-fashioned domestic magnetic resonance type 25 acidity meter with a minimum index of 0.1 units and the pHS-2 type acidity meter with a minimum index of 0.02 units. The pH value of such a pH meter is displayed by the meter pointer. The new digital pH meter has the domestic KL series of Kelilong, whose set temperature and pH value are displayed on the screen in digital form. No matter which pH meter is used before, it needs to be double-calibrated with standard buffer.
First read the instruction manual of the instrument, turn on the power, and install the electrode. Add a standard buffer of pH 7.0 to a small beaker, immerse the electrode, and gently shake the beaker to make the solution in contact with the electrode uniform. Read the pH of the solution according to the instructions attached to the different pH meter, check the pH meter to make the readings the same as the actual value of the standard buffer pH 7.0, and then stabilize the electrode; then remove the electrode from the solution and rinse it thoroughly with distilled water. Replace the small beaker with a standard buffer of pH 4.01 or 0.01, immerse the electrode, and repeat the above steps to stabilize the reading. This completes the two-point correction; after the calibration is completed, the electrode and the beaker are rinsed with distilled water. Do not rotate the positioning adjuster after calibration, otherwise it must be recalibrated.
Third, the use of acidity meter
The temperature of the solution tested should be the same as the temperature of the standard buffer. Therefore, the temperature regulator or the slope adjustment knob must be adjusted before use. The advanced pH meter has a temperature compensation system in the line. After the instrument is first corrected, it can automatically adjust the temperature change. • When measuring, first rinse the two electrodes with distilled water, gently blot the remaining solution on the electrode with filter paper, or wash the electrode with the liquid to be tested. Then, immerse the electrode in the beaker containing the solution to be tested, gently shake the beaker to make the solution uniform, press the reading switch, the value indicated by the pointer is the pH value of the solution to be tested, repeat several times until the value remains unchanged. A digital pH meter with a value change of less than 0.01 pH in about 10 s indicates that a stable reading has been reached. After the measurement is completed, turn off the power, rinse the electrode, and immerse the glass electrode in distilled water.
Fourth, the acidity meter maintenance and precautions
The glass electrode must be soaked in distilled water for more than one night before it is used for the first time. It should also be soaked in distilled water for use at any time. Do not touch the glass electrode with strong water-absorbing solvent for too long. Use it in a strong alkali solution as soon as possible. Wash it with water immediately after use. The glass electrode bulb is very thin and cannot be touched with glass and hard objects. When oil is contaminated, use alcohol, then carbon tetrachloride or ether, and finally soak in alcohol, then wash with distilled water. When measuring the pH of a protein-containing solution, the surface of the electrode is contaminated with protein, resulting in unreliable readings, unstable, and errors. The electrode can be immersed in dilute HCl (0.1 mol/L) for 4-6 minutes to correct it. . After the electrode is cleaned, it can only be gently blotted with filter paper. Do not wipe it with fabric. This will cause the electrode to generate static charge and cause reading errors. When the calomel electrode is used, be careful that the electrode is filled with potassium chloride solution, and there should be no air bubbles to prevent open circuit. A small amount of potassium chloride crystals should be present to keep the solution in a saturated state. When using, the rubber plug on the top of the electrode is removed, and a small amount of potassium chloride solution is discharged from the capillary to make the measurement result reliable.
In addition, the accuracy of the pH measurement depends on the accuracy of the standard buffer. Standard buffers for acidity meters require greater stability and less temperature dependence.