Ocean Optics Transmissive pH Probe - Manual (Page 3)

pH Probe Instructions
PH-BCG-TRANS-01-0210 3
For field measurements, the Ocean Optics handheld Jaz spectrometer offers an easy and portable
solution. An SD card contains a script that allows you to use the factory calibration or a complete
calibration, shows live pH values and provides the ability to save data right onto the SD card.
Probe Storage/Lifetime
Probes can be stored dry at room temperature for any amount of time. As they are used, the patches
may slowly leach indicator dye from the sensing material. As a rule, once the maximum absorbance
at pH 11 falls below 0.1, the patch should be discarded and replaced (assumes a reference of pH
1). The patch’s lifetime depends on frequency of use, harshness of the samples it is exposed to, the
temperature of samples, and other environmental factors.
Nature of Samples
The analyte solutions being measured should have a pH within the biological range (pH 5-9) for
accurate readings. Data obtained from analyte solutions that register values above or below this range
should not be considered valid within the specifications of the sensors. Aqueous solutions,
ethanol/methanol solutions, peroxides, ammonia, and sodium hypochlorite solutions are all compatible
with the sensor material. Samples being used with the transmissive probe should be optically
transparent, having no turbidity or sediment present. It is also ideal to have analyte solutions that are
colorless, though colored liquids can be compensated for.
Response time is dependent on the ionic strength of the solution, with higher salinity samples
responding notably faster. For example, using the calibration buffers of pH 5 – 8 will show a 90%
response in 10 seconds or less, but when pure D.I. water is being measured, more time is needed to
equilibrate at a final value. Make sure that the probe is sufficiently submersed into the analyte
solution, and that there are not bubbles present. To ensure no bubbles remain, shake the probe back
and forth through the liquid to knock them free. Likewise, more accurate results will be obtained if the
probe is rinsed once or twice with the analyte solution after calibration. This removes any residual
buffer solution that may contaminate your sample.
When immersed in solution, the film dyes may leach very slowly over time and will have to be
replaced. The film response rate is limited by diffusion of ions into the material; therefore increasing
stirring speed and ionic strength tend to increase the response rate.
pH Probe Set Up
The following procedures describe how to connect and calibrate the transmissive pH probe using a
VIS-NIR spectrometer, a light source and SpectraSuite software. See your spectrometer, light source
and SpectraSuite manual for more detailed installation information (available at
http://www.oceanoptics.com/technical/operatinginstructions.asp ).