How do syringe headspacers compare with loop/valve for senst

[MSCHemist]

I've been using a Tekmar 7000 for a while now. The best sensitivity settings for GC/MS have been 2ml loop, 5:1 split 1.3 ml/min He (~10ml/min) transfer line into the carrier feed.

I am in the process of setting up a MPS-II/CTC system and am curious how to get the best sensitivity for flavor scans with it. I can theoretically do splitless or pulsed splitless since I don't have a transfer-line to sweep. I assume a fast carrier flow and slow plunger to not overload the liner works best?

[RogerBardsley]

Thanks for all you work on the 7000. As the application chemist for Tekmar's headspace line, this is always good to hear. I can't offer much advice on how these compare. When you have your system up and running, I would like to hear how things are going. Please contact me at my company email, roger.bardsley@teledyne.com

[thohry]

I've been using a Tekmar 7000 for a while now. The best sensitivity settings for GC/MS have been 2ml loop, 5:1 split 1.3 ml/min He (~10ml/min) transfer line into the carrier feed.

I am in the process of setting up a MPS-II/CTC system and am curious how to get the best sensitivity for flavor scans with it. I can theoretically do splitless or pulsed splitless since I don't have a transfer-line to sweep. I assume a fast carrier flow and slow plunger to not overload the liner works best?

I have used both loop and syringe HS and it seems the syringe give a little better sensitivity.

[mckrause]

Splitless will not work. You still need to perform a split injection; it is a gas phase injection and you need to split it.

We use the fastest syringe settings we can get away with, and a low split (1:5) ratio. Depending on how light your light ends are you may need to go to a 1:10 or a 1:20 split.

I love the syringe injections - I much prefer them to the valve.

[Peter Apps]

Splitless will not work. You still need to perform a split injection; it is a gas phase injection and you need to split it.

This is too broad a generalization; if you can use stationary phase focussing and temperature programming to sharpen the peaks, then you can put 1 ml or more of headspace into the column without splitting, with considerable improvements in limits of detection. Also, with a megabore column running at high flows (say 10 ml/min) a 1ml injection is only 12s wide even if it is mixed 1:1 with carrier.

Peter

[MSCHemist]

When I do splitless I always use pulsed splitless that gives me a column flow rate of ~3-4 ml/min during injection. I tried pulsed split with my Tekmar 7000 but found the 6890 could not generate the low split pulses with acceptable reproducibility.

[mckrause]

Peter Apps wrote:

Also, with a megabore column running at high flows (say 10 ml/min) a 1ml injection is only 12s wide even if it is mixed 1:1 with carrier.

Peter, he specifically states he is using GC-MS. Hard, really hard, to run 10 mL/minute through your GC-MS.



I agree with the statement about the pulsed splitless. We have tried it in the past and found the variability to be high.

[Peter Apps]

Peter Apps wrote:

Also, with a megabore column running at high flows (say 10 ml/min) a 1ml injection is only 12s wide even if it is mixed 1:1 with carrier.

Peter, he specifically states he is using GC-MS. Hard, really hard, to run 10 mL/minute through your GC-MS.

True - I was broadening the scope. Nevertheless, a smaller volume injection with MS-compatible flows has the same logic.

Peter

[aldehyde]

This depends on application but I have traditionally had better sensitivity with a headspace plumbed directly into the split splitless inlet.