In order to calibrate a pH Sensor, or to confirm that a saved pH calibration is accurate, you should have a supply of pH buffer solutions that cover the range of pH values you will be measuring. 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, order code PH-BUFCAP, $29. 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 respective pH buffer solutions.
2. Flinn Scientific (www.flinnsci.com, Tel: 800-452-1261) sells a wide variety of buffer tablets and prepared buffer solutions.
3. You can prepare your own buffer solutions using the following recipes:
pH 4.00: Add 2.0 mL of 0.1 M HCl to 1000 mL of 0.1 M potassium hydrogen phthalate.
pH 7.00: Add 582 mL of 0.1 M NaOH to 1000 mL of 0.1 M potassium dihydrogen phosphate.
pH 10.00: Add 214 mL of 0.1 M NaOH to 1000 mL of 0.05 M sodium bicarbonate.