Chromatography Forum

Hey everyone,

I'm trying to develop a terpenes method in a hurry on a system that seems less than ideal for this analysis. I'm coming from an Agilent 7800 with a 7697A headspace sampler which is a pressure loop system. I'm now working on a Thermo TriPlus RSH. This is a static headspace system. I'm having troubles with carryover from the syringe and also high boiling terpenes (bisabolol and guaiol) seem to be getting caught in the syringe. They come out after doing IPA injections following standard injections. I really don't know how to go about improving this. The syringe and agitator oven temps are plenty hot enough. I'm not sure how else to avoid this. For carryover I was thinking I would inject less sample and decrease the split to put the same amount on column but less in the syringe?

Any help is much appreciated.

To avoid condensation of molecules in your syringe, your "equillibration" temperature (the temperature your sample has when extracting it with the syringe) needs to be lower than your syringe temperature (which in turn should have a lower temperature to your inlet). Try and see if you can detect your molecules at lower temperatures. If this isn't possible, then I believe you are correct in your assesment regarding the analysis method.

Do you have a split-splitless inlet available? If yes, I would definitely consider SPME to get at your terpenes. The sorbent is easily stripped of the previously trapped terpenes after the injection - getting you ready for the next injection. I use this technique to determine terpenes and terpenoids in alcoholic beverages. SPME offers a fairly wide range of accessible concentrations. It’s very good at determination of low concentrations in my samples.

If presented with the problem “detect terpenes in any sample”, I wouldn’t think of static headspace first.

If your sampler will do it, you can reduce carryover by dummy injections from an empty vial, or purging and pumping the syringe with inert gas or air.