Chromatography Forum

Hi,
Who has experience of using more than one type of headspace sampler?
Which one did you find the most suitable and why?
I measure extraction solvents in diluted plant extracts.
I currently have a Tekmar 7000 which I transport around to different GCs. I have great problems with the sample needle clogging with septa cores (I have to make sure I have plenty of flow before inserting into the GCs injection port).
I would love an integrated system - but how much is a PE headspace trap and Clarus GC?!
WK

I have used the PE HS-40 and the Varian Genesis (aka Tekmar 7000).

Both have advantages.

But your issue is with connecting to many GCs and moving the HS analyzer, is it not?

I would recommend that you do not use the GC injector at all if possible and to directly connect to your column via inert FSOT coated SS unions.

Of course you can directly connect to your gas supply going into the injector so you can still split your sample if needed.

The PE unit is much more complicated but has a lot less carryover than the Tekmar. Both are excellent tools and solid pieces of equipment in my opinion. Both can be utilized effectively if you change your method of bringing the sample to the column.

The PE unit may be easier to change amount of sample injected as it is a timed injection sampler rather than a fixed loop sampler like the Tekmar.

Rod

Thanks C1,
I didn't get any say in the purchase of the 7000 at the time.
Unfortunately at the moment I use the injector also for liquid autosampler injections too - so I am swapping back and forth every 2 days or so.

Has anyone tried to replace the old style sharp needle with a cone shaped autosampler needle? Did it create to much back pressure?

it should not be a problem.

The bigger issue is the dead volume going into an split splitless injection port, but if you have no problems with it, go adhead, and use a side port needle.

Rod

Thanks Rod,
I will try a pre-drilled septa today (ordered overnight - Supelco) and keep the injector nut/septa attached to the needle. Obvious fix I suppose.
Why I didn't think of this before I dont know!

I will then try to keep using the same transferline pressure knowing that the flow should be reasonably consistent (if PE autosystem pressure and split flow are the same each time).

Have you any other pneumatical (?!) ideas on the flow/pressure settings.
I have a CAP injector set at 7psi for a 30m x 0.25mm x 1.8um.
Split 25ml/min.

WK

Thanks for giving us your business. (Supelco)

When I was developing methods for HS analysis several years ago when I worked at Mallinckrodt, I chose to bypass the whole injector and go directly into the column. This improved my reproducibility and sensitivity.

I could do up to 1mL injections (details are in my paper published in AC June 1997) with my Tekmar 7000. I was one of the first beta testers of the deactivated components which worked so well.

Connecting the transfer line (FSOT SS tube) directly to the column via a deactivated SS union made changing instruments a breeze. I simply went into the GC oven just outside the injection port through the insulation.

One could go directly THROUGH the injection port via the septum nut as well.

Your solution should work well for you and you have the option of spitting your sample. I chose to modify the injection volume instead of dealing with the increase of 1% RSD the split injection produced, and was able to get stds at 100-5000 ppm to give me less than 1% RSD reproducibility for a wide range of analytes.

If I can be of additional help, feel free to contact me directly.

best wishes,

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

814-359-5737 voice
814-359-5459 fax
rgeorge@sial.com

Rod,
You must start work early in Bellefonte!
I always use LB2 as I have found them to be very reliable.
Thanks for the information.
I think I initially had problems with the transfer line pressure because of the core of septa in the needle.
I will update this thread when I get chance to try out my new set-up.
WK

Rod,
I have swapped this over 2-3 times now and its reproducible on my manual pneumatic CAP injector.
What would happen if I had to connect to a GC which had EPC?
Would it work or would the EPC keep trying to correct for the transfer line flow??
WK

I have not done this before. Sometimes EPC is not wanted. Perhaps you can set the flow on the PE to zero? and use the HS to furnish all the flow? Can you then set the split manually?

When I worked with this, I used the HS unit to furnish all flow through the GC. But I used Varian 3500 and 3400 and a HP 5890, so you see it has been a while.

I would assume that when you inject with the TEkmar there would only be a brief pressure pulse through the system and the EPC would not have time to react to a difference in pressure. But I don't really know.

Good luck.

Rod

If you want both liquids and headspace you can't do better than a CTC (Leap) CombiPal sampler. I have used several types of sampler CTC, Thermo that mimic manual headspace injection techniques rather than vial pressurisation and found they worked well.