Degassing-Filter Caps and Helium Sparging

Special Issues

Special Issues, Special Issues-04-01-2010, Volume 28, Issue 4

The answer to the following reader question about degassing mobile phase solvents was supplied by LCGC's "LC Troubleshooting" columnist John Dolan.

The answer to the following reader question about degassing mobile phase solvents was supplied by LCGC’s “LC Troubleshooting” columnist John Dolan.

Q: Just how good of a job do degasser–filter caps do on degassing HPLC solvent? Where can I find a technique or protocol to degas solvent with helium?

John Dolan: I have not seen data on the effectiveness of the caps, but I suspect that if you use them with a vacuum filtration device, they should be similar to vacuum degassing, which usually is adequate. Helium sparging is simple — just use a sparging frit (a solvent reservoir frit is fine) on the helium line — and bubble a stream of helium (for example, use 5 psi pressure) through the solvent for 4–5 min. Usually this is enough to keep the solvent degassed for a day. In difficult cases, or where any oxygen causes problems (for example, with reductive electrochemical detection), continuous sparging may be necessary. Just turn down the flow to a trickle to keep the solvent degassed. Most popular today are the in-line vacuum degassing systems, which are quite effective, but they might not remove sufficient oxygen for oxygen-sensitive methods.