Chromatography Forum

Hi All,
When you insert a new liner for SPME (or re-insert used liner)
do you bake out liner 20degC above operating temperature
for a while to "clean" it?
I have trouble with baseline for a while and also diethyl phthalate
which seems to accumulate.
Regards
WK

Hi WK,

Are you using special narrow-bore liner (0.75mm inner diameter) for SPME? Is it deactivated or not? Baking the liner after every replacement/cleaning is a standard procedure in my lab.
Did you check you injector septum for leaks or is there any possibility for its contamination during the replacement of the liner?

Regards

Hi Zokitano,
Thanks - I have residual DEP always it seems in SPME now and sometimes in split with wool. I use silanised 0.75mm liner and Chrompack BTO septa. No leaks - no contamination.
I used clean liner today which helped but baseline ramped still quite a bit.
So I also raised inj temp to 270 (+20) and some crud came off.
It was still a bit bad - but last thing tonight I removed old gas filter from gas line.
I will post tomorrow - hopefully that will improve baseline ramp - its the only plastic I have prior to GC (Varian Saturn 3800 GC). I have no hope of troubleshooting the pneumatics in that!!).
I used to use supelco green pre-cond. and have also used these Chrompack BTO and things have been OK with both which makes me think its liner or gas line related.
I haven't had chance to properly troubleshoot unfortunately.
What is your protocol for liner replacement?
Regards
WK

I am glad that you approached the problem systematically and hopefully it will be solved after the replacement of the old gas filter. Gas lines can carry contamination that has accumulated in the lines during the procedures of gas cylinder change. Also as you said maybe your old gas filter isn't doing its job anymore.
I suppose you're using MS detection (I have never worked on Varian Saturn system previously).

Regarding the protocol for liner replacement, I generally follow the instructions from the manufacturer (I work on Perkin Elmer Clarus 500 and Agilent 7890 GCs). Removing the septum nut first, and using a forceps to carefully remove the liner (and the o-ring around it) is the main procedure that I am using. But always do this with pair of fiber-free gloves put on, to minimize the contamination of the liner itself.

I also use TermoGreen septa from Supelco. So far haven't had any problems. I routinely check the inlet septum for any deterioration during SPME, because the SPME assembly needle piercing the septum has larger outer diameter than regular GC syringe needle has.

Hope this helps

Hi Zokitano,
All seems well this morning so far!
No DEP. On first run - initial baseline rise until 120degC and then tailed off.
No other septa/column type peaks either.
IMO I think it was the gas filter bleeding stuff in.
I use BIP cylinders anyway so it may not have been needed.
Regards
WK

Thank you for posting the outcome of your problem. I'm glad that you solved it.

Best regards

Hi Zokitano,
I have used SPME liner well but today I have to go back to wool packed liner for liquid injections.
So it takes about 4-5 hours to stabilize a new liner with new wool,new septa and new graphite seal.
I baked out liner for 30mins at 20degC above injector temperature and baked column for 30mins at 20degC above method upper temperature.
Even after this there was a bit of ramping early on but this disappeared after a few blank runs and in morning was OK.
Regards
WK

Hi Zokitano,
I have used SPME liner well but today I have to go back to wool packed liner for liquid injections.
So it takes about 4-5 hours to stabilize a new liner with new wool,new septa and new graphite seal.
I baked out liner for 30mins at 20degC above injector temperature and baked column for 30mins at 20degC above method upper temperature.
Even after this there was a bit of ramping early on but this disappeared after a few blank runs and in morning was OK.
Regards
WK

Hi WK

I presume now you're doing liquid injections with wool packed liner for SPME external calibration, because the volume of the SPME liner is too small to fit any reasonable liquid injection volume of the standard solutions.
Frequent changing of liners can couse serious headaches sometimes, especially if you need to maintain the GC-MS operating conditions for the analysis and you have to change the liner because of the different type of sample/standard introduction (e.g in SPME-GC).
The regular "preconditioning" of the liner is essential as you have already noticed, in order to minimize the potential interferring contaminants (added during the changing liner process).

Regards

Sorry Zokitano,
No I'm using different dimension liner for liquid injections. Nothing to do with SPME analysis.
Thanks for the help and advice.
Regards
WK

Hi Zokitano,
I have just replaced the liquid liner and put in the good previous SPME liner and I still get diethyl phthalate peaks. I changed septa type - still DEP.
So I used a brand new liner, graphite seal and hey presto no DEP - again a little baseline ramp which should go by tomorrow after a few cycles.
Shame then I have to keep using new liner each time at least for SPME.
Only thing I can think is perhaps when liner comes out of injector I put it back in the plastic tube it came in - could it pick up something from that - surely it would be there initially when first used?
I haven't studied just replacing the graphite seal yet - its possible that picks up something (is it like activated carbon??)
I will also store the SPME liner in a glass container when I remove it from the injector.
WK

HI WK

How are you handing the liners and other parts ? forceps, gloves ? If gloves, what material are they made of ?

Peter

Hi Peter Apps,
I am using stainless steel forceps and powder free white nitrile gloves.
WK

WK,

From your previous posts I can conclude that the contamination of the inlet is strongly related with the change of liners. I agree with Peter that inadequate handling of the liner during replacement process could put some contaminants. And the fact that you're observing DEP, it may come from some plastic material that was in contact with liners or eventually, phthalates are also present in air. So... there are different possibilities.
Systematically examine the whole liner replacement process to pinpoint the possible contamination source.

Regards

HI WK

This is where it starts getting nit picking and tedious , but if you can locate the cause of the problem it will be worth it in the long run.

Your plan to put the liner in a glass vial is a good one.

Try handling everything with forceps, this is fiddly, but I suspect the gloves.

Try another kind of glove - even a freshly washed cotton one. If DEP is a specific problem you might even be better off using fingers !

Have a clean tile, glass sheet or piece of stainless steel to put things down on. Never put anyting onto a painted, varnished or formica type surface.

Before you use the forceps heat them in a flame to ensure that all organics are removed (it destroys the forceps after a while but you are getting desperate right ?).

Good luck

Peter

Thanks all for the replies.
It gets frustrating. I can live with using new liner/seal/septa each time.
It's the wasted day in watching/trying to equilibrate it.
So next time I'll use a new liner/seal/septa but try and plan to leave it in overnight first.
Regards
WK