A calibration equation is stored on each pH Sensor before it is shipped. For the most accurate measurements with this sensor, we recommend you perform your own 2-point calibration with buffer solutions.

As the pH Sensor ages, the performance of the electrode will change and drift from the saved calibration. Good maintenance and recalibration of the pH Sensor will ensure the readings are accurate.

Preparing the pH Sensor for Calibration

First, remove the storage bottle and rinse the tip with DI water. Never wipe the sensing tip. Instead of wiping the sensing glass, you may blot the tip with a lint-free paper towel to remove excess moisture, but be extra careful not to rub the surface of the glass.

Preparing the Calibration Solutions

To do a two-point calibration for a pH sensor you will need two different pH buffer solutions. Your calibration is only as good as your knowledge of the reference values. For best results, the two calibration points should be widely separated and bracketing the range you anticipate in your experiment. For most chemistry experiments, we recommend buffer solutions of pH 4, 7, and 10. There are multiple ways to obtain these solutions:

  1. Vernier sells a pH buffer kit as pH Buffer Capsule Kit. The kit contains 10 tablets each of buffer pH 4, 7, and 10, and a small bottle of buffer preservative. Each tablet is added to 100 mL of distilled water to prepare the respective pH buffer solutions.
  2. Buffer capsules and prepared buffer solutions are also commonly available through a variety of chemical suppliers.
  3. You can prepare your own buffer solutions using the following recipes:

    1. pH 4.00: Add 2.0 mL of 0.1 M HCl to 1000 mL of 0.1 M potassium hydrogen phthalate.
    2. pH 7.00: Add 582 mL of 0.1 M NaOH to 1000 mL of 0.1 M potassium dihydrogen phosphate.
    3. pH 10.00: Add 214 mL of 0.1 M NaOH to 1000 mL of 0.05 M sodium bicarbonate.

Performing pH Sensor calibration

For the step-by-step instructions to calibrate the pH Sensor, see the list below.

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