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Why You Need to Look at Dispersive Liquid-Liquid Micro Extraction

Martin Perkins

1st November 2016

Dispersive Liquid-Liquid Micro Extraction, DLLME, Liquid-Liquid Extraction, LLE, MPS, MultiPurpose Sampler, Ray Perkins,


Automated DLLME using the GERSTEL MultiPurpose Sampler

 

In analytical sample preparation, Liquid-Liquid Extraction (LLE) is as old as the hills and in need of some fresh thinking.

Despite competition from newer extraction techniques, such as solid phase extraction, stir bar sorptive extraction and the like, LLE is still the go-to technique for sample extraction, clean-up and enrichment.  It is cheap, extremely adaptable and method development is pretty simple.

Which is not to say that it doesn’t have its problems; many of the most useful solvents are toxic, environmentally harmful and are becoming increasingly expensive to buy and to dispose of.

It is difficult to do without Liquid-Liquid Extraction, but we all have an obligation to do all we can to minimise its unpleasant side-effects.

Mass spectrometers become more sensitive all the time and every improvement widens our options concerning sample preparation; we can hit the same (or lower) limits of detection with smaller sample sizes and can often ditch slow and inconvenient enrichment steps.  However, it is a pain to redevelop and revalidate methods, so there is also an incentive to stick with the status quo.

On the other hand, if you are running lots of samples, the gains that can be made by switching to a cheaper, faster, fully automated variation of liquid-liquid extraction can far out-weight the costs of re-validation and if you are developing new methods from scratch, it makes sense to cash-in on the gains that are available from a more modern approach; which ever method you end-up using, you will have to validate it anyway.

Which brings us to the subject of Dispersive Liquid-Liquid Micro Extraction (DLLME) – if you haven’t come across it before, this is how it works…

  1. Lets assume that you have an aqueous sample.  First you select an extracting solvent that is immiscible with water (Trichloroethylene for example).
  2. Next, you chose a disperser solvent that is miscible with both water and your extracting solvent (Ethanol say).
  3. You make up a solution of your extracting solvent in the disperser solvent.
  4. You place a few millilitres of the aqueous sample into a sealed vial.
  5. You rapidly inject a few hundred microliters of the solvent mix into the aqueous sample.
  6. As the dispersing solvent dissolves in the water, so the extracting solvent comes out of the solution and forms a finely dispersed emulsion in the sample.  The extracting solvent has a massive surface area in contact with the sample and this brings about a rapid equilibration of analytes between the two phases.
  7. The equilibration can be helped by briefly vortex mixing the vial or by ultra-sonication.
  8. Finally, the vial is centrifuged in order to achieve full separation of the phases, prior to injection into the GC-MS.

The key points to appreciate about DLLME are:

  • DLLME retains all of the attractive features of traditional liquid-liquid extraction.
  • The whole extraction protocol can be automated using the GERSTEL MPS.  Manual errors are eliminated and the extraction process operates 24/7.
  • The amounts of solvent used are tiny (less to buy and less to dispose of).
  • The exposure of staff to toxic materials is minimised.
  • The process is very fast – often quicker than the run time of the GC-MS.
  • High degrees of enrichment are possible.
  • Consumable and labour costs per samples are tiny.

You can read more about DLLME here.

Right now, in the lab, we are busy with DLLME; we have several customers that want to explore its possibilities.

If you want to know more, or if you have a LLE method you would like to bring into the modern era, contact us on enquiries@anatune.co.uk, or call the office on 01223 279210.