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USING THE IQ150 PH METERS
USING THE IQ150 PH METERS
Traditionally, pH electrodes were based on fragile thin glass membranes that develop a small voltage in response to the adsorption of hydrogen ions from solution. In recent years, however, a new type of pH electrode called an “ISFET” has become popular. ISFET stands for ion selective field effect transistor. These electrodes are more robust than glass electrodes and offer the added advantage of being stored dry (i.e. no storage solution is required).A pH electrode must always be calibrated before measurements can be made. The procedures for calibration and making measurements presented below are taken from the IQ150 users’ manual. For more detailed information, see the full manual or visit www.phmeters.com.
Two-point Calibration:
You will need test tubes for the buffers, a beaker to collect waster, and a squirt bottle of RO water to rinse the electrode.
Obtain a bottle of pH 7 buffer and a bottle of either pH 4 buffer (if you’ll be measuring acidic solutions) or pH 10 buffer (if you’ll be measuring basic solutions). Fill each test tube approximately half full with the appropriate buffer.
Make sure the cap has been removed from the electrode, then rinse the electrode with RO water, shake it dry, and place it in the pH 7 buffer solution.
Press the ON/OFF button to turn on the meter.
5. If necessary, press the pH/mV button until the pH icon is seen on the display.
6. Press the CAL button.
7. If necessary, press the SELECT BUFFER button until the display matches the first buffer value (7.00).
8. Press the ENTER button. Wait for the large number display to stop flashing.
9. When complete, the meter will display the next stored buffer value. 2PT will also be displayed.
10. Rinse the probe with RO water, using the waste beaker to collect the water, then place the electrode in the second buffer solution.
11. If necessary, press the SELECT BUFFER button until the display matches the pH of the second buffer.
12. Press the ENTER button. Wait for the large number display to stop flashing. (If you get an error message, just repeat the entire calibration process. Sometimes it takes 2-3 attempts.)
13. pH Measurement
After completing the calibration procedure above, simply rinse the electrode with RO water and place it in the sample to be measured. Used calibration solutions can be poured down the drain.
When measurements are complete, replace the electrode cap and store the electrode dry.
Rinse all flasks and test tubes with RO water and place them back in the storage container.
NOTES:
NOTES:
If the electrode is new or has been stored dry for an extended period, soak the electrode in pH 7 buffer for at least five minutes before calibrating.
If calibration times are excessive (over 2 minutes), you should clean the electrode with a toothbrush and detergent (a few drops of dish detergent in a cup of warm water).
The lifetime of an ISFET electrode is anywhere from 18 months to 5 years. When it becomes difficult to calibrate (pH buffer value does not stop flashing during calibration or takes an excessively long time stop flashing), the electrode should be replaced. A probe that is dirty, miscalibrated, or has reached the end of its useful life will give an error message E06 or E07 on the meter display.
For the most accurate pH measurements, the calibration buffers should bracket the pH range being measured. Calibration buffer options are 1.68, 4.01, 6.86, 7.00, 9.18, 10.01, and 12.45. The calibration range, however should not be greater than 3 pH units.
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