PASCO PS-2147 High Resolution pH-ORP-ISE Amplifier - Manual (Page 3)

Calibrating the pH E lect rode:
A Practical App roach
CARD 2A
Calib rating the ISE/ ORP El ectrodes
Typically, pH electrodes are sensitive to the condition of the surface that is in
contact with the solution. Electrode performance depends on the history of
chemical treatment imposed on the critical measuring surfaces.
If the electrodes are kept in the appropriate solutions and not contaminated from
the solution or from evaporative deposits, they function well without calibration.
Calibration is often not needed for qualitative observations, especially where
concentrations of runs are being compared. If a quantitative result is desired for
calculation, or to compare to later results, then calibration is required.
Factory Calibration (no user intervention required): The sensor is calibrated at
the factory for a pH slope of -0.059 mV per pH unit and zero at a pH of 7.
Accuracies of 1.0 pH unit or better may be expected. This is the nominal slope for
a new pH electrode at 25 degrees C.
Full-Scale Calibration: pH calibration buffers of 4.0 and 10.0 are required for this
calibration. Accuracies of 0.1 pH units or better may be expected between 2.0 and
12.0 pH units after the full-scale calibration. (See the procedure on the right side of
this card.)
High Accuracy Calibration Procedure:
Very accurate pH measurements may be made with the PS-2147 if two basic
guidelines are followed: a) Select two buffer calibration solutions that closely
bracket the sample to be measured. b) Ensure the temperature of the calibration
solution is the same as the sample to be tested. To calibrate the sensor, follow the
calibration procedures outlined in the “Full-Scale Calibration Procedure”
instructions on this card; Be sure to insert the pH values of the buffers used.
Full-Scale Calibration Procedure:
With the sensor and electrode connected, do the following:
1. In DataStudio, click the Setup button on the main toolbar. The Setup
window will open.
2. Click on the pH Calibrate button in the Setup window. The Calibrate
window will open.
3. Rinse the pH electrode with deionized water and place it in the pH 4.0
buffer solution. Gently stir the electrode in the buffer solution.
4. Ensure the value in the dialogue box for Point 1 is 4.0. If using a different
solution, this value may be changed to the pH of the calibration buffer.
5. Watch the pH reading display in the dialogue box. When the pH reading
stabilizes, click the Set button adjacent to the Point 1 dialogue box.
6. Rinse the pH electrode with deionized water and place it in the pH 10.0
buffer solution. Gently stir the electrode in the buffer solution.
7. Ensure the value in the dialogue box for Point 2 is 10.0. This value may
be changed to match the pH of the calibration buffer.
8. When the pH reading stabilizes, click the Set button adjacent to the Point
2 dialogue box.
9. To save the calibration values, click the OK button. The calibration is
complete.
Specific calibration instructions for the ISE and ORP electrodes are included with
the electrodes. You will need to prepare or purchase specific standard solutions for
each ISE probe. Standard solutions can be purchased from any commercial
supplier of probe chemicals.
pH Calibration (continued)