A pH meter is a simple device to measure the acidity and alkalinity of a fluid. A pH meter is basically a sensitive voltmeter that accurately measures the voltage created between a reference electrode and a pH electrode. It displays the result in terms of the pH value of the solution in which they are immersed.
pH has a range between 0 and 14. Solutions with a pH=7 are neutral whereas those with pH<7 are called acidic and those with pH>7 are declared as alkaline.
HOW pH METER WORKS?
A pH meter consists of a probe, some processing electronics, and a display. There are two electrodes in a glass probe; one is a reference electrode and the other is a glass sensor electrode. They are hollow glass bulbs that contain a solution of potassium chloride with a wire of silver chloride suspended in them as electrodes.
The bulb of the sensing electrode is made of a special glass that is coated with metal salts and silica. As the bulb is dipped in a liquid the sensing electrode creates an electrical voltage due to the concentration of positive ions around the thin-walled glass bulb. This voltage is processed and calibrated to pH units and is presented on the display.
HOW TO CALIBRATE THE A pH METER?
Two or more standard buffer solutions of known pH are required to calibrate a pH meter. The standard buffer solutions are normally of pH 7.0, 4.0, and 10.0.
The procedure involves dipping the electrode into a buffer solution and then adjusting the pH meter to read the correct value of pH on the display. If the meter has an automatic calibration feature, then it will adjust itself automatically. This process is repeated with all the test buffers.
PROCEDURE FOR CALIBRATION OF THE pH METER
1. Select the calibration mode and set it at 100%. Also, set the temperature to 25°C. 2. Clean the electrode by rinsing it with deionized water and dry it completely with a tissue. 3. Dip the electrode in the pH 7 buffer solution, allow it to stabilize, then adjust the calibration knob to set the display to 7 and remove the electrode from the buffer. 4. Rinse the electrode with deionized water and dry it with a tissue. 5. Now dip the electrode in the pH 2 buffer solution, allow to stabilize and, then, adjust the calibration knob to set the display to 2 and remove the electrode from the buffer. 6. Rinse the electrode with deionized water and dry using a piece of tissue. 7. You may repeat the process with the solution of pH 10. 8. The buffer solutions should remain in their containers during calibration.
You should calibrate your pH meter with at least two points and one of them must be pH 7. You may calibrate for 3-points calibrations for better accuracy. There should be a difference of at least 2 pH units between any two buffers that are used. Asymmetry and slope can be determined for both 2-point and 3-point calibrations. 1-point calibration will only give you the zero point, but no slope. If you are using one 1-point calibration then use a buffer solution of pH 7.
PRECAUTIONS TO BE OBSERVED DURING CALIBRATION
Between each calibration point, the electrode and calibration container should be cleaned by rinsing with the solution that follows, as any remaining buffer solution may cause a measurement error. After you have finished calibrating to pH 7 and are preparing to calibrate to pH 10, then rinse the electrode with pH 10 solution.
You may also rinse the electrode with deionized water and carefully blot dry with a tissue. Ensure that the calibration container is always clean. The size of the calibration container is not important as long as the electrode is dipped in the solution completely.
Do not reuse buffer solutions for calibration. Once buffers are used for calibration, they are assumed to be contaminated and are discarded. Reusing buffer solutions can lead to errors in calibration.
Never use expired buffer solutions. Buffer solution bottles should never be left open, otherwise they may be contaminated.
Even CO2 in the air can contaminate the pH of the buffer solution. The buffer solution bottles should be opened very briefly and then shut again quickly.
Once you open a buffer solution bottle use it immediately.
Although it is not always essential it is best to start with a pH 7 buffer solution.
60 seconds is sufficient to achieve stability in readings with good electrodes. This response time can change depending on the age and cleanliness of the probe. A slower response is an indication that the electrode is dirty or old.
MAINTAINING THE PH METER
To ensure that your pH meter is in optimum condition, clean the electrodes carefully before and after use. This helps to maintain the accuracy and efficiency of your device. Dip the electrodes in the cleaning solution for 10 to 15 minutes and then rinse with distilled water or potassium chloride solution and store it in a safe place.
HOW SHOULD YOU STORE THE pH METER ELECTRODES?
The pH meter should be stored in clean and dry ambient conditions. The electrode should always be kept immersed in the recommended storage solution. This will ensure that the electrode does not get dry and will remain clean and ready for use.
Most pH meters are provided with a cap so that a small amount of storage solution can be added and it can be sealed. Or a storage bottle is provided which can be filled up with the storage solution. pH meters should never be stored in distilled water. Check regularly the level of the storage solution as it might evaporate over time. The electrode should never be left to dry out, as then it will not function correctly and will have to be replaced.
e2b calibration provides reliable and cost-effective calibration services for all types of pH meters both on-site and in our laboratory located in North East Ohio. Our verifiable and traceable services are unmatched in the industry. We are ISO-17025: 2017 compliant and registered with ANAB. We are also ANSI/NCSL Z540-1-1994 certified. Please contact us for all your calibration needs.