Ocean Optics OOISensors - Manual (Page 72)

4: pH Sensors
• Integration Period, Average, and Boxcar Smoothing are displayed for the active channel.
These values can be modified and will be used in the rest of the application if accepted.
Tip
Click on the scan button and optimize the integration period based on the spectra on the right side
of the screen. Monitor the spectra and adjust the maximum to peak to ~ 2500 counts. Average
should definitely be greater than 20; Boxcar should be around 10 to 20.
4. Block the light path and click the Dark button. OOISensors stores intensity (counts) values for all
wavelengths of interest.
5. Place the optrode in a low pH sample and allow the optrode to equilibrate for 10 minutes. Then,
click on the Low pH button to take its measurement.
• The Low pH measurement is the reference point for your absorbance measurements and
should be less than the lowest value in the linear range of the indicator. For example, for
phenol red a good reference pH would be 5. OOISensors stores intensity (counts) values for
all wavelengths of interest. These values serve as the reference values in the absorbance
calculations.
6. Place the optrode in a high pH sample and allow the optrode to equilibrate for 10 minutes. Then,
click on the High pH button to take its measurement.
• The High pH value should also be outside the linear range of the indicator. For phenol red,
pH 10 would be appropriate. An absorbance (AU) curve will be stored in the graph (red line).
OOISensors also stores values for all wavelengths of interest.
7. Place the optrode in a Low Buffer sample and allow the optrode to equilibrate for
10 minutes. The low buffer should be the same number entered earlier. Then, click on the Low
Buffer button to take its measurement.
An absorbance (AU) curve will be stored in the graph (blue line). OOISensors also stores values
for all wavelengths of interest.
8. Place the optrode in a High Buffer sample and allow the optrode to equilibrate for
10 minutes. Then, click on the High Buffer button to take its measurement.
• An absorbance (AU) curve will be stored in the graph (green line). OOISensors also stores
values for all wavelengths of interest.
Tip
The absorbance graphs for each measurement appear in the graph on the left side of the pH
Calibration screen. The intensity measurements appear in the graph on the right side. Pay
attention to the intensity measurements. A sudden overall drop in intensity may be attributed to a
bubble, particularly when using the transmission probe. If an increase is noticed where there is a
saturation of the detector, you must drop the integration time and restart the calibration from Step
4.
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