Degassing Liquids with Freeze-Pump-Thaw Cycling
Source: Laboratory of Dr. Neil Branda — Simon Fraser University
Degassing refers to the process by which dissolved gases are removed from a liquid. The presence of dissolved gases such as oxygen or carbon dioxide can impede chemical reactions that utilize sensitive reagents, interfere with spectroscopic measurements, or can induce unwanted bubble formation.
A number of different techniques are available for degassing liquids; some of these include heating, ultrasonic agitation, chemical removal of gases, substitution with inert gas by bubbling and freeze-pump-thaw cycling. Freeze-pump-thaw cycling is a common and effective method for small scale degassing, and will be demonstrated here in more detail.
- First, place the desired solvent or solution into a Schlenk flask and close the stopcock (Figure 2a). Seal all other openings on the Schlenk flask. Caution: do not use more than 50% of the volume of the flask and inspect the flask for cracks or fractures. An overfilled or broken flask may shatter during the process.
- Attach the flask to a Schlenk line and keep the corresponding valve on the Schlenk line closed. Freeze the liquid completely by submerging the flask into a Dewar containing liquid
The removal of dissolved gases is important in both academia and industry. It is often required for maintaining the quality of machinery and laboratory instruments, for protecting various chemical reactions, and obtaining accurate readings for chromatography and spectrophotometry.
Reactions that use or generate air sensitive reagents, for example, organometallic compounds, thiols, phosphines, and electron rich aromatics frequently require some level of degassing to maintain their integrity thr
- Shriver, D. F., Drezdn, M. A. The Manipulation of Air Sensitive Compounds. 2nd ed. Wiley & Sons: New York, NY (1986).
- Girolami, G. S., Rauchfuss, T. B., Angelici, R. B. Synthesis and Technique in Inorganic Chemistry: A Laboratory Manual. 3rd ed. University Science Books: Sausalito, CA, (1999).
- Kotz, J., Treichel, P., Townsend, J. Chemistry and Chemical Reactivity. 8th ed. Brooks/Cole: Belmont, CA. (2012).
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