8 Ways to Increase the Sensitivity of Headspace Sampling

Martin Perkins

23rd February 2012

Headspace analysis is important to many industries

The analysis of low levels of volatile organics is increasing in importance

Of late, we have had a steady stream of people asking us how to get more sensitivity from headspace sampling. In most cases, the analyst has made a good job of optimising the vial chemistry, has fine-tuned the instrumental parameters and still doesn’t have enough horsepower.

If you are in this position, here are some ideas you can consider.

The figure in brackets represent the approximate gain you can expect to make, compared to the best that static headspace sampling can achieve.

  1. Fit a cryotrap between your injector and column and inject larger headspace samples in splitless, rather than split mode. (x10).
  2. Convert your system to dynamic headspace sampling (DHS).  This is easy if you have a GERSTEL MultiPurpose Sampler (MPS). If you have a CTC/Agilent CombiPal, it can be converted into an MPS and then upgraded. (x20).
  3. If you have a suitable instrument to hand, try purge & trap sampling. This gives similar gains to dynamic headspace sampling (x20).
  4. Try Stir Bar Sorptive Extraction in headspace mode (HSSBSE). This drives the equilibrium in the right direction, stripping analytes from the matrix. Good for slightly heavier compounds. Good sensitivity due to splitless injection (x10).
  5. If you have plenty of sample available, use Large Volume Headspace – the Entech 7150 concentrator is able to sample hundreds of grams of sample, collect hundreds of milliliters of headspace, cope with large amounts of water, focus all of the analytes and inject everything onto the column without splitting. This is the sledge-hammer solution. If this doesn’t work, then nothing will. (x100).
  6. If you think your problem is due to analytes partitioning too weakly into the headspace, try fully evaporative headspace (FET) to eliminate the effect of the matrix (variable, can be x10).
  7. If your problem is that you can’t pick out your analytes from the matrix background, consider heart-cutting to separate target analytes from chemical noise. A great way of boosting S/N.
  8. Some of these gains are additive, so consider combining some of these ideas (DHS with heart-cutting for example).

Our applications lab is set-up with all of this instrumentation and we have used all of these techniques successfully, at one time or another.

So if you have the problem of insufficient sensitivity in headspace mode, by all means give us a call on 01954 212909, or email enquiries@anatune.co.uk  for more information.  If we can help you, we will.