Scientists levitate water droplets to look for contaminants

May 3 (UPI) -- It turns out it's easier to find heavy metal contaminants in water when droplets are levitated using sound waves.

Trace amounts of heavy metals are difficult to measure, but even tiny amounts can be dangerous. Thus, detecting metal toxins is essential to protecting human health.

"Despite the large variety of water sensors that offer continual monitoring, detection of multiple heavy metals dissolved in water can only be performed by sending samples off for specialized laboratory analysis," Victor Contreras, a physicist at the National Autonomous University of Mexico, said in a news release. "Our new technique is one step toward the development of a simpler analysis approach that could be applied on-site and in real time. This type of water analysis could be used by agricultural, pharmaceutical, water purification and other industries to monitor water for contaminants."

To identify contaminants, scientists used laser induced breakdown spectroscopy. By levitating water droplets with sound waves, scientists can isolate the evaporation process and increase the concentration of contaminants in the tiny sample.

Using the technique, researchers were able to identify small amounts of barium, cadmium and mercury. The analysis process takes just a few minutes.

Laser induced breakdown spectroscopy uses a high-energy laser pulse to vaporize the droplet and produce a plasma. The plasma absorbs the light and reemits unique wavelengths. Encoded in these wavelengths are the spectral signatures of different molecules, thus, revealing the sample's chemical composition.

Usually, scientists place a water sample on a substrate, like a slide disk, and allow it to evaporate. This lets them uses a slightly smaller and more energy-efficient laser, but it takes a while. As well, water evaporation can allow impurities to contaminate the sample and interfere with the analysis.

Scientists solved the problem by levitating tiny drops of water with sound waves.

"Acoustic levitation is a simple and inexpensive method to preconcentrate the elements of interest while avoiding contamination from the substrate surface," said Contreras. "Moreover, it does not require the sample to have any type of electric or magnetic response like some other methods used to achieve levitation."

Researchers detailed their new methodology in a paper published Thursday in the journal Optics Letters.