The use of pH meter and precautions

The pH meter is a precision instrument for measuring pH and can also be used to measure electromotive force.

1. How to use (1) Installation 1 The voltage and frequency of the power supply must be in accordance with the data indicated on the instrument's nameplate 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. (2) Calibration 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.

(3) Measurement 1 The excess water on the electrode should be sucked dry or washed twice with the tested solution, then the electrode should be immersed in the tested solution, and gently turn or shake the small beaker so that the solution can 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.

2. Precautions (1) Prevent the instrument from coming into contact with moisture. Immersion of moisture will reduce the insulation of the instrument, making it less sensitive, accurate, and stable.

(2) The glass film of the glass electrode ball is extremely thin and easily damaged. Avoid contact with hard objects.

(3) The glass film of the glass electrode should not be stained with oil. If it is accidentally stained with oil, it can be washed with carbon tetrachloride or ether, rinsed with alcohol, and finally washed with distilled water.

(4) The presence of air bubbles in the potassium chloride solution of the calomel electrode is not allowed, and there is little crystallization to maintain saturation. If there is too much crystallization and the pores are clogged, it is best to add new saturated potassium chloride solution.

(5) If the pointer of the pH meter has serious jitter, replace the glass electrode.

3. Preparation of Standard Buffers The reagents used in the standard buffer used in the pH meter are easily purified and stable. The commonly used preparation methods are as follows:

(1) Standard buffer with pH=4.00 Weigh 5.07 g of potassium hydrogen phthalate which was dried at 105° C. for 1 hour, dissolved with distilled water, and set the volume to 500 ml.

(2) Standard buffer of pH=6.88 Weigh 3.4001 g of potassium dihydrogen phosphate (KH2PO4) dried at 130° C. for 2 hours, disodium hydrogen phosphate (Na2HPO·12H2O) 8.95 g or disodium hydrogen phosphate anhydrous (Na2HPO4). 3.549g, add distilled water to dissolve and set the volume to 500ml.

(3) Standard buffer with pH=9.18 Weigh 3.8144 g of sodium borate (Na2B4O7·10H2O) or anhydrous sodium borate (Na2B4O7) 2.02 into distilled water and dissolve to volume. Drying ovens and incubators Drying ovens are used for dry and dry heat sterilization of articles. Incubators are used for the cultivation of microorganisms and biological materials. The structure and usage of these two instruments are similar. The use temperature range of the drying oven is 50~250°C. The common fan type electric heating is used to accelerate the temperature rise. The maximum operating temperature of the incubator is 60°C. 1. How to use (1) Insert the thermometer into the seat (at the top of the deflate regulator in the top of the box).

(2) Plug the power plug into a power outlet.

(3) Turn the head of the heating wire group to the 1 or 2 position (depending on the required temperature). At this time, the blower can be turned on to promote hot air convection. After the group of electric heating wires is turned on, the red indicator light is on.

(4) Observe the thermometer. When the thermometer temperature will reach the required temperature, adjust the automatic temperature control knob, so that the green indicator light just shines, and then observe the thermometer and indicator light after ten minutes. If the temperature on the thermometer exceeds the need, and the red indicator light is still on, then Turn the automatic temperature control knob slightly counter-clockwise until the temperature is constant at the required temperature. The indicator turns red and green. The thermostat knob is on the upper left side of the front of the case. Its scale plate cannot be used as a temperature standard indicator and can only be used as a marker for adjustment.

(5) In the constant temperature process, if there is no need for three groups of heating wires to generate heat simultaneously, only one set of heating wires may be turned on. The more open groups, the faster the temperature rises.

(6) After working for a certain period of time, the top central deflation regulator can be opened to vent the moisture, and the blower can also be turned on.

(7) After use, switch all the heating wire grouping switches off and turn the knob of the automatic thermostat counterclockwise to zero.

(8) Unplug the power plug.

2. Precautions (1) Check the power supply before use and have a good ground.

(2) There should be no explosion-proof equipment in the drying oven. Do not heat flammable materials and volatile materials in the box. Do not place flammable items near the cabinet.

(3) The inside of the box should be kept clean, and the ware should not be rusted, otherwise it will affect the cleanliness of the glassware.

(4) It should be monitored at regular intervals during use to avoid affecting the use of temperature or accidents.

(5) Blower motor bearings should be refueled once every six months.

(6) Do not twist the temperature sensor inside the box. Avoid touching the temperature sensor when placing items. Otherwise, the temperature is unstable.

(7) Cut off the power supply during maintenance.