Analysing Volatile Leachables with the use of Automated Headspace Solvent Micro-Extraction (HSME)

Martin Perkins

28th January 2014

If you are currently using Solid Phase Micro Extraction (SPME) then this new headspace sampling technique will almost certainly be of interest.
As you will be aware, SPME is a popular GC sampling technique that uses a polymer coated fibre as the extraction medium. The changing from one type of fibre to another, changes the selectivity of the sampling process and the range of functionalities you can use is limited to what is commercially available.
Headspace Solvent Micro Extraction (HSME) is similar to SPME in many ways, but offers one big advantage that SPME lacks – with HSME, you are free to define the nature of the extraction medium and so the specificity of HSME is more tuneable than SMPE.

What Is HSME?

HSME is a four-step process:

  1. Incubation – the sample is placed in a sealed headspace vial and allowed to equilibrate.
  2. Enrichment – a tiny drop of solvent is suspended from the tip of a syringe in the headspace of a solid or liquid sample, and analytes in the headspace migrate into the solvent.
  3. Recovery – the solvent micro-drop is pulled back into the syringe needle and the needle removed from the vial.
  4. Injection – the solvent is injected into a GC or GC-MS for analysis.

The development of HSME

There are a number of considerations that have been taken carefully into account with the development of this process. First, with regard to the syringe, there are some specifications that ensure accuracy of HSME. The needle tip of the syringe should have a relatively large surface area so that the micro-drop can be readily recovered into the barrel of the syringe.
The properties of the solvent should also be carefully considered. For instance, the solubility of target analytes in the solvent should be adequate to ensure that recovery is possible. Additionally, the boiling point of the solvent should be such that it will not evaporate during the process of extraction. Good choices for extraction solvents include 1-octanol, ethyl decanoate and  n-hexadecane.

Automating HSME

Until now, HSME had been carried out manually, but this is inefficient and subject to poor reproducibility due to drop-to-drop variations. In order to overcome these issues, the technique has been automated using the GERSTEL MultiPurpose Sampler (MPS) controlled by a special version of GERSTEL Maestro software developed through a partnership between Glaxo SmithKline, Anatune, and GERSTEL.
A study was performed using this system, and it was found to greatly increase reproducibility and sample processing efficiency.

Important uses of HSME

One of the main benefits of HSME is the fact that the solvent can be tailored to deal with the particular analytical challenges of each scenario in question.
Different solvents have different effects on recovery of the analyte. It is also important to control the extraction temperature based upon the target analyte; for example, highly volatile analytes are more easily recovered at lower temperatures.
Its primary use of HSME will be to pinpoint the risks of various substances leaching from substances used to manufacture, transport, or package pharmaceutical products. This application is discussed in this poster presented at Extractables and Leachables Europe 2013; a conference organised by Smithers Rapra in London last December.
However, HSME has great potential in many other fields and should be of general interest to anyone currently using SPME.
What do you think?
If you have a potential application and would like to know more, please call +44 (0)1223 279210 or email: