I'm using an accumet basic AB15 pH meter to measure citrate-phosphate buffers. I accidentally re-standardized the probe using the provided pH 4.00 buffer without deleting my previous calibration. I believe this forced the pH meter to calibrate to pH 2.0 instead of 4.0. Now, everytime I try to calibrate the meter using pH 4.0, it automatically corrects the reading to pH 2 instead of pH 4.0. I've tried this multiple times, deleting the calibration each time, tried turning it off and on, cleaned the probe, used fresh buffer, and tried measuring from pH 10 to 7 to 4. Each time I dip the probe in the pH 4 it first reads as pH 4 but when I standardize it, it shifts the reading to pH 2. I currently don't have access to a pH 2 buffer. Any tips? Thanks!
Calibration of the Meters with pH 7 and pH 2 Buffers
1. Select the pH Mode and set the temperature control knob to 25°C. Adjust the cal 2 knob to read 100%.
2. Rinse the electrode with deionized water and blot dry using a piece of tissue (Shurwipes or Kimwipes are available in the labs).
3. Place the electrode in the solution of pH 7 buffer, allow the display to stabilize and, then, set the display to read 7 by adjusting cal 1. Remove the electrode from the buffer.
4. Rinse the electrode with deionized water and blot dry using a piece of tissue (Shurwipes or Kimwipes are available in the labs).
5. Place the electrode in the solution of pH 2 buffer, allow the display to stabilize and, then, set the display to read 2 by adjusting cal 2. Remove the electrode from the buffer.
6. Rinse the electrode with deionized water and blot dry using a piece of tissue (Shurwipes or Kimwipes, as before).
Measuring pH
1. Make sure that the meter is set to the pH Mode and adjust the temperature to 25°C.
2. Place the electrode in the sample to be tested.
3. The pH of the solution appears in the display.
NOTE: Allow the display to stabilize before taking your reading!
4. Rinse the pH electrode and place it back in the storage solution.
Reference:-
http://chemed.chem.purdue.edu/genchem/lab/equipment/phmeter/use.html
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