Fizzy extraction brings out semivolatile compounds | Chemical & Engineering News
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Web Date: September 2, 2016

Fizzy extraction brings out semivolatile compounds

Extracting semivolatile compounds with carbon dioxide bubbles reduces the need for heat and solvents
Department: Science & Technology
News Channels: Analytical SCENE, Organic SCENE
Keywords: analytical chemistry, chemical extraction, semivolatile compounds, carbon dioxide, supercritical fluid extraction
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Fizzy extraction works by flushing a sample with CO2 (left), allowing it to sit for a minute while stirring under pressure (center), then depressurizing the sample (right), allowing the gas, including extracts, to escape into a mass spectrometer for detection.
Credit: Anal. Chem.
Photograph of extraction vials at three stages in the fizzy extraction process.
 
Fizzy extraction works by flushing a sample with CO2 (left), allowing it to sit for a minute while stirring under pressure (center), then depressurizing the sample (right), allowing the gas, including extracts, to escape into a mass spectrometer for detection.
Credit: Anal. Chem.

When Pawel L. Urban cracked open a soda on the beach in southern Taiwan last summer, he suddenly became aware of the soda’s aroma wafting up to his nose. The analytical chemist from National Chiao Tung University thought that if carbon dioxide bubbles could bring out the soda’s aroma molecules, perhaps that same idea could be applied in the lab to do chemical extraction.

Now, Urban has done just that, reporting a new technique to extract semivolatile compounds from liquids based on the phenomenon of effervescence (Anal. Chem. 2016, DOI: 10.1021/acs.analchem.6b02074). The technique, which Pawel dubs “fizzy extraction,” operates at room temperature and provides sample analysis within seconds of bubble formation.

“It is a fantastic idea,” says Miguel de la Guardia, an analytical chemist at the University of Valencia not involved in the study. “It is a simple and fast procedure.” Traditional methods typically require heat to liberate the semivolatile compounds, consuming energy and exposing samples to potential chemical reactions that can interfere with sample analysis.

Urban designed and built a small fizzy extraction system, and his graduate student Cheng-Hao Chang tested it on a range of samples with different volatilities, including ethyl acetate, caffeine, limonene, and extracts from lime juice and peel. They first placed a water-ethanol solution of each sample in a glass vial and flushed the space above the liquid with CO2 for about a minute. Then, they maintained 150 kPa of CO2 pressure in the space for another minute while vigorously stirring the sample solution, saturating the solution with the gas. Opening a valve allowed the system to depressurize quickly, producing lots of bubbles that immediately carry the semivolatile compounds in each sample into a connected mass spectrometer.

For highly volatile compounds such as ethyl acetate, or nonvolatile compounds like caffeine, fizzy extraction doesn’t increase their gas phase concentration for analysis, Urban says. But for semivolatile compounds such as limonene found in lime juice and peel, fizzy extraction increases their gas phase concentration by up to 20-fold. Urban believes fizzy extraction could be useful for chemical analysis in the food and beverage sectors, as well as in environmental remediation.

De la Guardia would like to see fizzy extraction being tested on a larger variety of samples and its energy and solvent consumption evaluated. Meanwhile, Urban is working to understand the mechanism. He speculates that fizzy extraction works because the semivolatile compounds have some affinity for the carrier gas, in this case CO2, and stick to the bubbles in the instant that they form. To that end, Urban plans to test fizzy extraction using different carrier gases.

 
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Comments
Jerry King (September 7, 2016 3:43 PM)
Not to much new here really - people working in the lower pressure regime using SC-CO2 extraction have known and shown this for many years, the highly negative cross virial coefficients between semi-volatile organic compounds and pressurized CO2 predict viable extraction as described in the literature over 30 years ago.
Pawel Urban (September 8, 2016 11:10 AM)
Thank you for the comment. We know about SFE, which uses a high pressure of CO2 to extract compounds. Here, quite a low pressure was used (150 kPa). The solutes were released due to effervescence. They left the sample within few seconds, what produced a high signal in real-time mass spectrometry. This is advantageous for analytical applications. I believe SFE remains the gold standard for preparative work, though.

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