Ocean Optics Smart pH Cuvettes User Manual

Smart pH Cuvettes Instructions

Overview

The Fiber Optic pH Sensor system consists of the following:

 Smart pH Cuvettes (1 cm x 1 cm PMMA or quartz) and/or patches
 Ocean Optics VIS-NIR spectrometer (or Jaz Sensor module)
 SpectraSuite software for reading values
 Light source (LS-1 Tungsten Halogen Light Source with a blue filter or a white LED)
 CUV-UV Cuvette Holder
 Connecting Fibers

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).

The Smart pH Cuvettes use a sol gel sensing material coated onto the inner walls of a cuvette. The
immobilized indicator dye(s) are encapsulated into the sol gel matrix, allowing for the diffusion of
ions while preventing leaching of the dye. The cuvettes provide very accurate measurements in the
biological range, from pH 5 to 9. Advantages of these cuvettes over traditional potentiometric devices
include faster response time, easy storage and no maintenance, and low cost. These are especially
useful for monitoring low conductivity samples such as boiler water, where electrode devices fail.

Ocean Optics’ fully integrated pH systems provide full spectral analysis to help eliminate errors from
dye leaching or from changes in turbidity, temperature, and ionic strength. Inherent calibration based
on the physical properties of the immobilized indicator dye eliminates the need for frequent
calibration. The ratiometric algorithm provides accurate and reproducible measurements at a high
resolution.

Smart pH Cuvettes are 1 cm by 1 cm and are made of Poly(methyl methacrylate) (PMMA) or quartz.
The PMMA material has a temperature range of -5 °C to 70 °C, while quartz is available for specific
applications such as high-temperature measurements. The cuvettes are compatible with aqueous
solutions, ethanol/methanol solutions, ammonia, peroxides, sodium hypochlorite solutions, while the
quartz cuvettes are also compatible with concentrated acids (nitric, sulfuric, acetic, etc) and acetone.

Although PMMA cuvettes are designed to be disposable, they can be used multiple times. The lifetime
depends on the extent of exposure to high pH levels and harsh chemicals. See

Storage/Lifetime for more information.

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Cuvette

Smart Cuvettes Instructions

Cuvette Storage/Lifetime

Smart Cuvettes can be stored dry at room temperature for any amount of time. As they are used, the
cuvettes may slowly leach indicator dye from the sensing material. As a rule,

absorbance at pH 11 falls below 0.1, the cuvette should be discarded and replaced

reference of pH 1). The cuvette’s lifetime depends on frequency of use, harshness of the samples it is
exposed to, the temperature of samples, and other environmental factors.

once the maximum

(assumes a

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 cuvette. Concentrated acids and acetone
will ruin the plastic cuvettes, so these types of chemicals should be avoided. Aqueous solutions,
ethanol/methanol solutions, peroxides, ammonia, and sodium hypochlorite solutions are all compatible
with the sensor material and the plastic cuvette. Samples 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 cuvette is filled to a sufficient level with the analyte
solution. If the liquid level is at or below the optical path, the data will not be valid. To ensure there is
sufficient liquid, it is recommended to fill the cuvette about 70% its height. Likewise, more accurate
results will be obtained if the cuvette is rinsed once or twice with the analyte solution after calibration.
This removes any residual buffer solution that may contaminate your sample. Note that once the
cuvette has been affixed into the cuvette holder, it should not be moved or removed until all
measurements have been completed.

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 Smart Cuvette Set Up

The following procedures describe how to connect and calibrate pH Smart Cuvettes using a VIS-NIR
spectrometer, a light source and SpectraSuite software. See your spectrometer and SpectraSuite
manual for more detailed installation information.

Installing the pH Sensor System

► Procedure

Perform the steps below to install the pH Sensor components:

1. Install SpectraSuite on your computer.

2. Connect the spectrometer to your computer using the supplied USB cable.

3. Install the light source as specified in its instructions.

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Smart Cuvettes Instructions

4. Attach the fibers between the spectrometer, cuvette holder, and light source.

5. Turn on the light source and allow it to warm up for the period specified in the light source
instructions.

Caution

Make sure that the cuvette says fastened in the cuvette holder with the tightening
screw and that it does not move until all measurements have been completed.
Any movement will change the optical signal, disrupting the quality of the
measurement.

Calibrating the pH Sensor System

The Smart Cuvettes include a pre-calibrated pK value determined at the factory. This value was
originally obtained at 22°C, and it is recalculated using the temperature compensation algorithm based
on the temperature that was entered in SpectraSuite’s Calibration Wizard. Using the Factory
Calibration method is ideal for being able to start making pH measurements quickly, though it is less
accurate than performing an Independent Calibration. The specifications listed for the cuvettes assume
a complete Independent Calibration, as this eliminates the errors seen from temperature and other
environmental differences.

Using Factory Calibration

► Procedure

1. Open SpectraSuite and select File | New | New Sol Gel pH Measurement.

2. Click the Calibration Wizard button to begin the calibration.

3. Select the spectrometer to use and click

4. Select

Use Factory Calibration and click Next. The Experimental Parameters screen appears.

Next.

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