Simple, Inexpensive and Novel Sample Preparation for LC-MS

Martin Perkins

11th December 2011

Not a lot of people know this…

Twister Back-Extraction for HPLC and LC-MS

SBSE back-extraction can be readily automated

Stir Bar Sorptive Extraction (SBSE) is a very handy way of preparing samples for analysis by LC-MS and if you only work with LC, you will probably never have heard about it.

With SBSE, the extraction medium takes the form of a magnetic stir bar coated with a thick, polydimethyl siloxane film. To extract an aqueous sample, you simply whizz up the stir bar in the sample for an hour or two, and all but the most polar compounds partition into the PDMS film.

If it’s the volatiles that you are after, then you rinse the stir bar with distilled water, blot it dry and thermally desorb the stir bar into a GC-MS. However, SBSE extracts organics of all kinds, even those that run on LC and the stir bars can be conveniently back-extracted into an organic solvent, ready for injection into an LC.

So what are the benefits to you as an HPLC user?

  • High throughput – you can run as many extractions in parallel as necessary.
  • The process enables you to perform an extraction of an aqueous sample and end up with the analytes in a water miscible solvent (like acetonitrile).
  • The process is effective in cleaning up dirty samples for LC, removing many sources of ion suppression and enhancement.
  • Only a small volume of solvent is used to extract the stir bar and most of the extract can be injected into the LC-MS.
  • This works well with both large samples (500ml say) and small (< 1 ml).
  • The stir bars can be reused hundreds of times.

If this sounds interesting and you would like to give it a go, I have a limited number of trial kits that I can let you have for free. If you want one of these then email: