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How to Measure Dissolved Oxygen
Wednesday, August 19, 2020

Did you know that many industries use dissolved oxygen? Besides, there a few methods for how to measure dissolved oxygen when you need to know its value.

Why would you test for dissolved oxygen? The answer to this relies on what industry you work. For example, a winemaker and lab technician monitor dissolved oxygen (DO), but the reasons are very different. Keep reading to learn more about how to measure dissolved oxygen in liquids.

What is Dissolved Oxygen?

Dissolved oxygen is a measurement of how much oxygen is dissolved in water or other liquids. In water, it tells us how much oxygen is available for aquatic organisms like fish. When we know how much is in a stream or lake, it reveals a lot about water quality.

In wine-making, the goal is to keep oxygen levels as low as possible. When there is too much oxygen, it causes white wines to turn brown, and overall, the flavor in either white or brown is degraded.

Methods of How to Measure Dissolved Oxygen

When you need to test for dissolved oxygen, there are few methods you can use to do so. You can choose from chemical tests, membrane sensors, or newer types like optical sensors.

Titration - The Winkler Method

This method is the most common and was developed by Hungarian analytical chemist Lajos Winkler in 1888. The Winkler Method is a renowned process of measuring the amount of dissolved oxygen in water and is extremely accurate.

You begin with 300 ml of water measured into a stoppered flask. Using a calibrated pipette, you add 2 ml of manganese sulfate and 2 ml of alkali-iodide-azide to the water sample. Then you place the pipette with its opening just below the water's surface; this helps avoid introducing bubbles into the sampled water.

Stopper the bottle so that no air gets trapped under it. If you note any bubbles, discard the sample and begin again. An orange-brown precipitate will form if there is oxygen in the water.

The Membrane Sensor Technique

The simplicity of using a membrane sensor makes it a popular system. Instead of needing to collect water samples, you simply put the sensor in the water where you find it. Traditional dissolved oxygen sensors use electrochemical cells separated from the water by membranes. These come in two versions, polarographic and galvanic.

The Optical (fluorescent) Sensor

The optical sensor is a newer technology and uses many principles that are much different from those used for galvanic or polarographic probes. A fluorescent material interacts with the oxygen in the water, and this is related to how different wavelengths of light affect it.

There are some significant advantages over traditional methods with this type of sensor. For example, there is less maintenance required as there is no membrane or filling solution to replace.

What's Next in Dissolve Oxygen

Learning more about how to measure dissolved oxygen is essential if you are in an industry where monitoring and controlling oxygen in liquids is needed. When you need to know more about the devices that help measure oxygen, you can turn to Analytical Technology.

They've made it their goal to help their customers get the knowledge they need to ensure a healthy and safe environment. If you have questions, get in touch with them today.

From our U.S. headquarters in Collegeville, Pennsylvania, we design, manufacture, and distribute analytical instruments based on electrochemical and optical sensors. We specialize in the areas of toxic gas detection and water quality measurements, continuing to lead the way in development of reliable monitoring systems. Our capabilities in the area of sensor design and manufacture allow us to offer the kind of application support needed for the most demanding applications. In addition, local product support is available through our network of over 50 representatives throughout the U.S. and Canada.

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