Precautions for measuring samples with a digital pH meter

If so, reconstitute the pH meter specification buffer.

Plug the shorting plug or the electrode plug when not in use. The electrode plug and socket of the pH meter must be clean and dry. To prevent dust and moisture from entering, the input impedance of the instrument is reduced, which affects the measurement accuracy.

Different samples should be selected for the appropriate pH electrode (eg measuring strong acid, strong base or pure water). >

The lead wire of the electrode must be kept stationary while the sample is being measured. Do not touch with your hands. Otherwise it will cause unstable measurement.

Its conductivity should be less than 2 μ S/cm zui for good boiling. It is necessary to use twice distilled water or deionized water to prepare the standard solution. >

The alkaline solution should be packed in a polyethylene bottle and sealed tightly. The standard buffer should be stored in the refrigerator (low temperature 5 10 °C), to ensure the accuracy and reliability of the standard buffer. It can usually be kept for 2 to 3 months. If it is found to be turbid, moldy, or precipitated, it cannot be used.

Do not return the used specification buffer to the standard reservoir. Do not use a standard buffer that exceeds the shelf life. Standard timing. And the temperature of the calibration solution is as close as possible to the temperature of the sample.

Whenever possible, use a standard buffer close to the pH of the sample.

The zui is turned off and then turned on again, and the electrode is replaced during the use of the instrument. Recalibrate.

2 . 2 Electrode use precautions

The composite electrode should not be temporarily immersed in distilled water, 2 . 2 Precautions for electrode use < Composite electrodes should not be temporarily immersed in distilled water. When not in use, the electrode should be inserted into the bottle containing the electrode protection solution to keep the electrode bulb in an active state.

Dissolve in 250 ml of ionic water, then add 56g of analytically pure Kcl. Prepare the electrode protection solution: Take pH 4.00 buffer (250ml one bag. Stir until completely dissolved.

The electrode head should be prevented from colliding and the electrode cover should be removed. In order to prevent the glass bulb of the electrode from rupturing, the electrode is invalidated.

It should be noted that the reference liquid in the electrode is reduced, when using the dosing electrode. If it is less than 1/2 volume, it can be added from the upper hole with a dropper. When measuring, the sealing sleeve should be moved downward to expose the small hole.

Wash the electrode with distilled water before moving the electrode from one solution to another. Drain the water with filter paper. Do not deliberately wipe the glass bulb of the electrode, otherwise the electrode response may be slow. A good method of zui is to rinse the electrode with the liquid to be tested.

If there are bubbles to shake the electrode, prevent air bubbles in the reference solution inside the electrode. Make it clear.

Especially when measuring a solution with a very low degree of dissociation (such as pure water) and when the temperature of the solution is low or the electrode is aged, the response time of the instrument is related to the internal resistance of the electrode, the temperature of the solution, and the nature of the solution. The indication time of the instrument will be longer.

Wash carefully after use. A good way to choose zui is to choose an E314 composite electrode. Test strong acid, strong alkali or special solutions (such as: containing protein, paint and other solutions) should minimize soaking time. >

The slope and response speed of the electrode will decrease. The electrode bulb can be diluted with 0.1mol/L dilute HCl solution (preparation: 9ml HCl diluted with ionized water to 100ml for 24 hours, after the electrode is temporarily used. If the passivation is serious, the electrode bulb can be immersed in 4% HF solution. (Preparation: 4ml HF is diluted with ionized water to 100ml for 35 seconds, washed with distilled water, and then immersed in electrode maintenance solution to make it recover properly. If neither method can restore it, please replace the electrode.

The emulsion, when the sample solution contains substances that easily contaminate sensitive bulbs or block the reference electrode liquid junction (such as suspended matter, viscous liquid, etc.) will passivate the electrode. The phenomenon is that the sensitivity is reduced, or the reading drift is unstable and misaligned. In this case, it should be washed with a suitable solution according to the nature of the pollutants, then the solvent should be washed away with distilled water, and placed in the electrode maintenance solution to be soaked.

Cleaning methods for pollutants: for reference)

Contaminant cleaning agent

Inorganic metal oxide concentration less than 1mol/L dilute acid

Organic fats and oils

Resin polymer substance alcohol, acetone, ether, etc.

Protein blood cell sediment acid enzyme solution (such as food mother tablets)

Pigment materials, dilute bleach, hydrogen peroxide, etc.

If using a cleaning solution that will dissolve the polycarbonate, note: when using a cleaning agent. For example, carbon tetrachloride, trichlorohexene, tetrahydrofuran, etc., it is possible to dissolve the polycarbonate resin (electrode material) on the sensitive glass bulb, and the electrode is invalid, please use with caution!

2 . 3 General fault inspection and judgment

Not the instrument itself. In addition, most measurement problems occur due to electrode failure or measurement method errors. Standardizing the use of buffers , samples and many other factors can also lead to problems, please analyze carefully to determine the problem

instrument

The simple method of zui is to connect the short-circuit plug of the instrument to the electrode socket of the instrument (must ensure good contact). When the pH is measured, adjust the temperature to 25 °C to judge whether the instrument is normal. After pressing CA L, the pH value of the instrument should display 6.86 mV. When the CA L is pressed, the mV value of the instrument should display 0.00. Press the YES button. The pH lamp or “mV lamp flashes for a few seconds and then goes out. The value remains the same. You can judge that the instrument is basically normal. If it is not normal, please check with your supplier or Ark.

electrode

When testing with the electrode, if the instrument is judged to be normal. The indication is unstable or the instrument response is slow; the reproducibility is poor; or it cannot be calibrated to the desired pH, please check the electrode:

Whether the ends of the electrode leads are loose or broken; whether the connectors are good. >

Whether the electrode bulb is immersed in the sample;

Whether there are bubbles in the solution in the electrode;

Whether the electrode bulb is contaminated;

Please replace the new electrode. If this is the case.

Specification buffer

The reading is incorrect or cannot be calibrated if the main unit and the electrodes are normal. Please check the buffer solution:

Do not use the correct pH specification buffer;

Check if the buffer has exceeded the shelf life or is inconsistently contaminated;

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