Vernier pH sensor
pH sensor should never be stored in distilled water. It is a good idea to prepare a quantity of pH 4 buffer/KCl storage solution (see the section on Maintenance and Storage) and use it to replace lost solution.
Calibration
For many experiments, calibrating the pH Sensor is not required. We store a calibration equation on each pH sensor before shipping it, which is used as a default by our software.
For the most accurate measurements with this sensor, we recommend calibration. It is a simple process that takes only a few minutes.
Calibrate the pH Sensor Using LabQuest
- Connect the pH Sensor to your LabQuest. The pH reading will be displayed.
- Choose Calibrate > CH1 : pH from the Sensors menu and tap Calibrate Now.
- Remove the storage bottle from the pH Sensor, rinse the tip of the sensor with distilled water, and place the sensor in the first buffer solution so the tip is immersed.
- Enter the pH of the buffer solution as the known value for Reading 1. When the voltage reading stabilizes, tap Keep.
- Rinse the pH sensor with distilled water and place it in the second buffer solution.
- In the Reading 2 field, enter the pH of the second buffer solution. When the voltage reading stabilizes, tap Keep.
- (Optional) If you wish to store the calibration on the sensor itself, tap the Storage tab at the top of the screen. If you wish to use the calibration only for the current experiment, skip to Step 9.
- On the Storage page, tap Save Calibration to Sensor. A message will appear: “Saving this calibration to the sensor will result in it being the new Custom Calibration 1”. Tap OK to proceed.
- Tap OK to complete the calibration process.
After you store a calibration to the pH Sensor, this new calibration will be used automatically, regardless of the interface to which the pH Sensor is connected.
You can set the pH sensor back to its factory calibration by following these steps:
- Choose Calibrate > CH1 : pH from the Sensors menu.
- Tap the Storage tab.
- Tap Restore Sensor Factory Defaults.
pH Buffer Solutions
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.
- Vernier sells a pH buffer kit (order code PHB). The kit contains 4 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.
- Flinn Scientific (www.flinnsci.com, Tel: 800-452-1261) sells a wide variety of buffer tablets and prepared buffer solutions.
- 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. |
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