Liquid Membrane Extraction (LME)

Liquid Membrane Extraction (LME) relies on either a pH gradient or a solvent gradient to facilitate extraction. The pH in the sample is adjusted to render the analyte neutral (uncharged), which encourages its passive transport into the organic SLM.

Compared to electromembrane extraction (EME), LME is conceptually simpler and easier to develop methods for. However, LME is generally slower and suitable for a narrower range of analyte properties. Unlike EME, LME can also be applied to analytes that cannot be ionized.

How does it work?

Organic solvent membrane

1. Two separate vials

Two separate vials holding the sample solution and the acceptor solution.
Organic solvent membrane

2. Organic solvent membrane

The vials are separated by an organic solvent immobilized in the pores of a polymeric membrane, called the supported liquid membrane (SLM).
pH or Solvent gradient

3.  pH or Solvent gradient

LME relies on either a pH gradient or a solvent gradient to facilitate extraction. The pH in the sample is adjusted to render the analyte neutral (uncharged), which encourages its passive transport into the organic SLM. Conversely, the pH in the acceptor solution is modified to ionize the analyte, driving the equilibrium favorably towards the acceptor solution.

Alternatively, or in conjunction with a pH gradient, a polar organic solvent like methanol or DMSO may be added to the acceptor solution. This solvent adjustment creates a favorable distribution equilibrium without needing analyte ionization.
Pure sample extracted

4. Pure sample extracted

You now have pure sample extract. Under optimized conditions, LME can provide very clean extracts with reduced matrix effects i.e. a complete discrimination of proteins and phospholipids, reducing down-time of your MS instruments. The extracts can be injected directly on LC-MS instruments using very short LC-methods before MS.