A pH meter, used in labs the world over, is used to measure the acidity or alkalinity of a substance. Although some meters are now so advanced that you can easily fit them into your pocket, these necessary pieces of equipments are still delicate instruments that require careful calibration before use.
Instructions
1. Prepare your buffer solutions. You will need 3 to 4 clean beakers. One of these beakers should remain empty, and the second should be filled with a calibration buffer of pH 7. Your third beaker should be filled with a solution suited to how you plan to use your meter: pH 4 (if you plan to measure acidic solutions) or pH 10 (if you intend to measure base solutions). If you intend to use the meter for a wide range of solutions, you may need all three buffers.
2. Inspect your pH meter. Your meter should be clear of any algae or salt deposits, cracks, or anything that may interfere with a clear reading. Once you've inspected your meter, you may have to set the meter's temperature. Some meters may do this automatically, whereas others may need the temperature input manually, after you've measured it by way of a thermostat. In that same vein, you should make sure that your buffers are at room temperature (25 degrees C).
3. Use a wash bottle to rinse the meter in distilled water into the first empty beaker. You should always perform this step before you place the meter into a new solution, to minimize contamination. Shake off the excess water, and ready your beaker filled with pH 7 solution.
4. Immerse your meter in a pH 7 solution, taking care to both fully immerse the electrode and not to hit the bottom of the beaker. Allow your meter to calibrate automatically to the solution (on older meters, you may have to manually turn a calibration knob until your meter reads 7). Calibration will take anywhere from several seconds to a minute. If the readings oscillate widely, you try examining the meter's junctions and cables, or try another electrode.
5. Rinse off the electrode with distilled water into the first beaker, and repeat Step 4 for the pH 4 buffer. When calibrating to the second solution with an older meter, you may need to calibrate with a second knob. Repeat this step again with ph 10 buffer if necessary (with a third knob). Meanwhile, remember that high pH buffers quickly absorb atmospheric carbon dioxide. Use pH 10 solution as quickly as possible, and don't leave the bottle open to the air.
6. Re-calibrate your pH meters regularly, as often as every week if you use your meter every day. Keep an eye out for when your meter starts to suffer from low batteries, as diminished battery strength will interfere with the accuracy of your readings. You may also want to clean your meter every month with a custom pH electrode-cleaning solution.
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