More on Degassing Mobile Phase Solvents

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

Now that helium costs are high, our labs are considering switching to hydrogen as a carrier gas in our gas chromatography applications. Do you think it is necessary to maintain helium in the laboratory solely for sparging mobile phase? Can nitrogen be substituted?

John Dolan: Unfortunately, nitrogen will not work for degassing high performance liquid chromatography (HPLC) mobile phases. Nitrogen does displace the oxygen, but its solubility characteristics are such that it causes outgassing problems — this is why we degas in the first place, to get rid of nitrogen and oxygen. An alternative that many laboratories use today are the in-line degassers that are offered with most new HPLC equipment and can be purchased as after-market add-ons for your system. For most cases, these work fine. If you have a method that is very sensitive to oxygen (for example, electrochemical in reductive mode), you will need to use helium sparging, but for most other applications the in-line vacuum degasser will work fine. There are many laboratories that have these and never use helium sparging.

Questions?

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