pH meter installation, adjustment and measurement

The pH meter is abbreviated as a pH meter (acidity meter) in daily life. It is mainly composed of an electrode and an electricity meter. PH meter must be able to properly maintain the electrode in use, according to the requirements of the preparation of standard buffer and the correct operation of the electricity meter, in doing so, can greatly reduce the pH indication error, thereby improving the reliability of chemical experiments, medical test data. Therefore, as a precision instrument, the PH meter is very important to use, and daily maintenance must be carefully prepared.

First, install

1 The voltage and frequency of the power supply must conform to the data indicated on the nameplate of the instrument and must be grounded. Otherwise, the pointer may be unstable during measurement.

2 The instrument is equipped with a glass electrode and a calomel electrode. The bakelite cap of the glass electrode was clamped on the small clip of the electrode holder. The calomel electrode's metal cap was clamped on the large clamp of the electrode holder. The height of the two electrodes can be adjusted using the head screws on the electrode holder.

3 Glass electrodes must be soaked in distilled water for more than 24 hours before initial use. Should not be soaked in distilled water.

4 The calomel electrode should be soaked in saturated potassium chloride solution before its initial use. Do not soak it in distilled water with the glass electrode. When not in use, soak in saturated potassium chloride solution or cap the lower capillary of the calomel electrode with a rubber cap.

Second, schooling

1 Turn the pH-mv switch to the pH position.

2 Turn on the power indicator light at the beginning and warm it up for 30 minutes.

3 Remove the small beaker of distilled water, and use the filter paper to gently remove the excess water on the glass electrode. In a small beaker, select a standard buffer solution of known pH. Immerse the electrode. Note that the capillary of the glass electrode tip and the calomel electrode are immersed in the solution. Gently shake the small beaker so that the electrode is in contact with the solution.

4 Screw the range switch to 0-7 or 7-14 depending on the pH of the standard buffer.

5 Adjust the temperature control knob so that the temperature indicated by the knob is the same as the room temperature.

6 Adjust the zero point so that the pointer is at pH 7.

7 Press lightly or slightly turn the reading switch to make the switch jam. Adjust the positioning knob so that the pointer is exactly at the pH value of the standard buffer. Release the reading switch and repeat until the value is stable.

8 After alignment, do not turn the positioning knob again, otherwise it will need to be re-aligned. Remove the standard small beaker and rinse the electrode with distilled water.

Last, measurement

1 The excess water on the electrode is sucked dry or washed twice with the solution to be tested, then the electrode is immersed in the solution to be measured, and the beaker is gently rotated or shaken to make the solution evenly contact the electrode.

2 The temperature of the test solution should be the same as that of the standard buffer solution.

3 Zero calibration, press the reading switch, the value indicated by the pointer is the pH of the test solution. If the pointer reading exceeds the scale when measuring in the range of pH 0~7, the range switch should be set to pH 7~14 and measured again.

4 After the measurement is completed, after releasing the reading switch, the pointer must be at pH 7, otherwise readjust.

5 Turn off the power, rinse the electrodes, and soak as described above.

When using the pH meter method, it is also necessary to correctly understand the electrode usage of the pH meter. At present, the electrodes used in the laboratory are all composite electrodes. The advantages are that they are easy to use, free from oxidizing or reducing substances, and have a faster balance. In use, the rubber sleeve and the rubber sleeve at the bottom of the electrode filling port are completely removed to maintain the hydraulic pressure difference of the potassium chloride solution in the electrode. Here's a simple introduction to the use and maintenance of the electrode:

1. When the composite electrode is not used, it can be fully immersed in 3M potassium chloride solution. Never wash with wash solution or other absorbent agents.

2. Before use, check the bulb at the front of the glass electrode. Under normal conditions, the electrode should be transparent and free from cracks; the bulb should be filled with a solution and no bubbles should be present.

Second, special attention should be paid to the temperature of the solution to be tested before calibrating. In order to correctly select the standard buffer, and adjust the temperature compensation knob on the power meter panel to make it consistent with the temperature of the solution to be tested. The pH of the standard buffer solution is different at different temperatures.

After calibration is completed, the instrument does not need to be calibrated again within 48 hours for frequently used pH meters. If one of the following conditions is encountered, the instrument needs to be recalibrated:

(1) When there is a big difference between the solution temperature and the calibration temperature;

(2) The electrode has been exposed to air for a long time, such as more than half an hour;

(3) The positioning or slope regulator is mis-operated;

(4) After measuring the solution of peracid (pH<2) or overbase (pH>12);

(5) After changing electrodes;

(6) When the pH of the measured solution is not in the middle of the selected solution when the two points are calibrated, and is further away from 7 pH.