How to Degas a Solution Using an Ultrasonic Bath

By Aimee O'Driscoll, 09 April 2021

Liquids naturally have gases trapped inside them, but these trapped gases can be undesirable for many applications. Dissolved air can negatively impact chromatography applications, for example. Trapped gases can also affect the intensity of ultrasonic cavitation, lowering the efficiency and effectiveness of a variety of processes such as cell lysis and ultrasonic cleaning.

Thankfully, degassing solutions is relatively straightforward, especially if your bath is equipped with a degas feature. In this article, we explore more about why we might need to degas solutions and how to do this using an ultrasonic bath.

Why We Need to Degas Solutions

There are a number of reasons you may want to remove dissolved gases from solutions. A common one is to remove trapped air from the mobile phase used in liquid chromatography applications. Gases dissolved in the liquid can impact the flow of samples through a column, compromising the integrity of the results.

Another use case is to remove air from oxygen-sensitive samples. Excess oxygen could cause unwanted chemical reactions such as oxidation, or impact desired reactions. It could also encourage microbial growth in certain samples.

One more case in which you may need to degas liquids is when testing the viscosity and density of viscous liquids such as gels or shampoos. Viscosity results can be thrown off as the viscometer will see less resistance from gases. Density results will be impacted as air is obviously far less dense than a liquid or semi-liquid sample, throwing off pycnometer results. 

In addition, many processes that take place in an ultrasonic bath can benefit from having a degassed solution. For example, when using an ultrasonic tank for cell lysis, lipid extraction, dispersion, emulsification, or cleaning, you’re relying on the intensity of ultrasonic waves.

When you use an ultrasonic bath, you’re seeing a process called cavitation. A transducer at the base of the bath creates ultrasonic waves that cause the formation and collapse of bubbles. The force resulting from the collapse of these cavitation bubbles cleans objects, lyses cells, and more.

Trapped gas inside the cleaning solution absorbs some of the ultrasonic energy, inhibiting the cavitation process. A 2013 study showed that cavitation intensity is significantly increased in degassed water compared to regular tap water. This means that when using a degassed solution, your ultrasonic process will be more powerful and likely more efficient.

How to degas solutions

Many ultrasonic baths offer a degas mode. This is highly convenient for degassing an ultrasonic cleaning solution as you simply pour the solution in the bath and run the unit on degas mode before placing your objects in.

Even if an ultrasonic bath doesn’t have degas mode, you could simply run it on a normal cycle to get rid of the trapped gas. It just might take a little longer as degas mode speeds things up by switching between full and low power to drive bubbles to the surface.

When degassing samples, you can place the sample inside a vessel (such as a beaker or flask) and then position the vessel in the ultrasonic bath (that’s filled with solution). You may be able to rest the vessel on a tray in the tank or you could use a stand and clamp to hold it in place.

A degas cycle can take as little as 10 minutes, but it depends on what liquid you’re trying to degas (for example, viscous liquids will take longer to degas), how much gas is dissolved in it, the volume of the liquid, and how much ultrasonic power you’re using. You can usually tell that degassing is complete as bubbles stop rising to the surface.

Note that heat can speed up the degassing process as the solubility of gases is inversely proportional to temperature. This means that warming the solution can cause the bubbles of trapped gas to go to the surface more quickly. If you’re degassing viscous liquids, heat can help by decreasing the viscosity of the liquid as well as lowering the solubility of the gas. Many Branson ultrasonic cleaners have heating capability.



Bransonic ultrasonic baths.

The Bransonic 0.5 Gallon Ultrasonic Bath comes in a heated and unheated version.