Hi I'm Gerard Sharp. Welcome to the May 2011 issue of the monthly newsletter. This month the Tech Tip is on Optimising Peak Shape for Splitless Injections.

Dr Gerard Sharp...

Ardent Scientific has just launched a new Chromatography eLearning site full of interactive multi media training modules with voice overs explaining the content as you go along. There's lots of free content so click here to view. Enjoy!


 

Tech Tip - GC Splitless Injections

Getting better peak shape for GC splitless injections

My observation of chromatograms from labs throughout Australia carrying out GC splitless injection is that the peak shape, especially for the early eluting peaks (volatile compounds), can be excessively broad (as shown in this chromatogram). Broad peaks will lead to a loss of resolution and poor quantitation. However, there is a simple fix. Change the type of inlet liner you are using.

Essentially, there are three aims of a good GC inlet liner:


 

  • Vaporise the sample quickly
  • Transfer the sample vapor to the column quickly
  • Ensure the sample doesn’t degrade in the process

 

By choosing a small inner diameter inlet liner, chromatography for the volatile components can improve dramatically. The reason for this is the reduction in diameter results in a smaller liner volume and leaving all other conditions the same (i.e. the inlet pressure and therefore the column flow rate), the velocity of the carrier gas through the liner is increased. Therefore, the vapour cloud, which results from the sample injection, is transferred faster from the liner to the column. This has the effect of sharpening peaks and leads to better sensitivity and quantitation. The transfer rate from liner to column of the late-eluting (semi-volatile) components is less important because of cold trapping when using a temperature programmed method and so a wider diameter liner is often OK. This is the reason wide liners are often described as both 'split / splitless' but narrow liners only as 'splitless'. The drawback for a narrow diameter liner can be you are more limited to the liquid volume of sample that can be injected into the GC and vapour flash back has to be considered.


The typical diameter for split injection for an Agilent Technologies liner is 4mm and this should be reduced to 2mm when doing splitless injection for volatile compounds.


eLearning

 

Chromatography eLearning is yet another way to enhance your chromatography knowledge. While not ever being able to replace a classroom course, eLearning does offer advantages on cost and rich interactive content.  

Also, unlike a classrom course you can learn at your own pace and return to the content time after time.

Ardent Scientific offers varying levels of membership for viewing eLearning content. The Single Membership starts at $300 / year and corporate memberships are also available. View here for full details.

 

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P.O. Box 549, Box Hill Vic 3128, Australia ph 0422 872 212
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