Ocean Optics OOISensors - Manual (Page 67)

Chapter 4
pH Sensors
Overview
The Fiber Optic pH Sensor system consists of a fiber optic probe designed to hold immobilized indicator
dye materials, a light source, a spectrometer, and OOISensors software. Calibration requires recording
spectra in high and low pH samples, as well as in at least one pH standard solution (such as a NIST-
traceable buffer).
pH Films
The Fiber Optic pH Sensor System uses two different types of films: Transmissive and Reflective.
Transmissive indicator dye films are used for clean, transparent samples. Reflective indicator dye films
are used for turbid or absorbing media.
Each type of film consists of a cellulose mechanical matrix surrounded by a hydrophilic polymer that
entraps the indicator molecule. The films are stable when stored dry, and are suitable for nearly any
aqueous sample environment.
When immersed in water, the film dyes may leach very slowly over time and will have to be replaced.
The film response rate is slow (on the order of minutes), being limited by diffusion of ions into the
material. Increasing stirring speed, ionic strength, and temperature all tend to increase the response rate.
Probe Options
The following sections detail options available for the Fiber Optic pH Sensor probes.
TP300-UV-VIS Probe
The TP300-UV-VIS probe is a chemically inert PEEK polymer transflection probe that can be equipped
with a special tip (RT-PH) for mounting transmissive films in the optical path. Light is directed via one
fiber through the mounted film to a mirror. The light is then redirected back through the film to a receive
fiber that returns the light to the spectrometer. The sample is free to flow over the sides of the film.
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