How do we measure dissolved oxygen?

How do we measure dissolved oxygen?

We can measure dissolved oxygen through iodometry, colorimetry, electroanalytical methods, and luminescence.

Iodometry

Iodometry is a form of titration.  An iodometry titration is a titration method where the appearance or disappearance of iodine is used to signal the end of the titration. The titration used for determining the concentration of DO is called the Winkler Method. This provides a “one-time measurement” of your sample.

Colorimetry

Colorimetry is a measurement of color. We use chemical reagents to react with the DO sample, and they form a particular color. The intensity of the color is directly proportional to the amount of DO in your sample. The reagents used in colorimetric tests are similar to a modified version of the Winkler Method. This method provides a snapshot of what is going on in your sample with DO.

Electroanalytical Methods

Electroanalytical methods are quite simply, dissolved oxygen probes. The two types of probes that use this type of chemistry are called galvanic and polarographic, and they work based off of oxidation-reduction (redox) reactions. Either probe will provide continuous, live-time measurements for monitoring your samples. Before we discuss the electrodes, first let’s do a short review of the redox reactions.

Optical Dissolved Oxygen

Optical Dissolved Oxygen still uses a probe to measure the dissolved oxygen, the probe, and meter-monitor luminescence. Simply, there is a blue light emitted by the probe, and the blue light excites the light-sensitive material in the probe cap. As the material calms back down, it releases a red light, and it is measured when it hits a light sensor. If dissolved oxygen is present, it will suppress the red light. The intensity, lifespan of the light (decay), and frequency of the red light are all dependent on the concentration of oxygen. Optical dissolved oxygen probes are also able to provide a continuous measurement of your sample.