Ask the Editor: Replacing Acetonitrile

The answer to the following question was provided by LCGC’s “LC Troubleshooting” columnist John Dolan.

Q: Since acetonitrile is in short supply and the prices have sky-rocketed in recent months, what can be done about replacing this solvent with others for various chromatography applications?

A: Unfortunately, there is no solvent that is a simple replacement for acetonitrile. It will require a rework of the method — perhaps with a change in the column, but certainly the mobile phase organic solvent and perhaps additives.

A better alternative to pursue is acetonitrile conservation. Most liquid chromatography systems can be used quite well with 2.1 mm i.d. columns. So a 150 mm x 4.6 mm column operated at 1 mL/min can be replaced with a 150 mm x 2.1 mm column at 0.2 mL/min. A further savings can be accomplished by going from a 150-mm, 5-µm particle column to a 100-mm, 3-µm particle column, for a reduction in retention time of 30%. The combination of these should reduce solvent consumption to 100/150 x 0.2/1 = 13% of the original. And most well-plumbed conventional systems can accommodate this without the added expense of new equipment. And there is an added bonus of increased sensitivity (peak height) if you can load the same mass on the column (may or may not be true).

Questions?

LCGC technical editor Steve Brown will answer your technical questions. Each month, one question will be selected to appear in this space, so we welcome your submissions. Please send all questions to the attention of "Ask the Editor" at lcgcedit@lcgcmag.com We look forward to hearing from you.