HELP!! Contamination in my system after changing the septum!

[pollypocket78]

Hello all,

Hope somebody here will have an answer for me.

It's been one month now that I can't analyse anything because of the presence of a peak in each of my analysis.

It started the day I changed the septum, as a very common maintenance, I did it the same way as usual etc...
Then on the next blanks I passed, there was this intense DEP peak and some small peaks of DOP and dimethyl phtalate.

Since then, the engineer in charge of my GCMS and I have been trying to : change the septum, the insert, the whool, cleaned and replaced the traps, change the column, change the gas bottle, the syringe... We ran a lots of blank analysis each time, with or without injection of solvent (I usually use ethanol), and with acetone as well. We tried to run only the MS and only the GC.

It seems to come from the GC not the MS. AFter all these trials, I don't know what's left to do... Do we have to change anything else in hte injection port?

The DEP peak keeps the same intensity and never decreases. Except when we programmed a special method high temperature to volatilise the DEP which is supposed to vaporize at 299deg. But afterwards, it never disappeared totally and it was back the same as before.



If you ever meet this problem before and/or have any suggestion, you are most welcome to express them here !!

Thank you in advance!

Delphine

[Don_Hilton]

Did you change anything else while you were replacing the septum? Like tighten or replace a fitting between the gas bottle and the back of the GC? Or change gas cylinders?

And is the gas supply dedicated to this instrument or is it shared?

[pollypocket78]

No, I really did only this septum maintaining. Something I do once a week actually!

The changing of my gas cylinder has been done 2 weeks after, the contamination was already there.

[pollypocket78]

The gas supply only goes to this GCMS indeed, we are a small laboratiry

[Rolandas Plausinaitis]

If it is a normal peak -- it is from GC - injector or gas supply (to have a shape of a peak it has to pass trough column).

Model/configuration of the instrument might give someone a clue.

Could some particles torn away from the septum by syringe fall into injector during the septum change?

Did you check septum purge flow is still OK?

Was septum from a new bottle or batch?

Does split ratio change influence the area?

[pollypocket78]

Hello,

The model and configuration of my GCMS system is :

Shimadzu QP2010 PLus. 1 non polar column. It had been run for a year without any pb.

I actually found a pb about the syringe just after changing the septum (after a few batch files), the syringe was "torn", and I had to replace it because it was not possible to inject correctly anymore. So maybe some particles fell indeed into the injector. But the engineer from Shimadzu has been cleaning it several times so that's weird.

So I purchased a new syringe, changed the septum and ran a lot of others trials. Same result.

The septum was supposed to be a nice long-life one. Not a new batch though but it's true that I don't use them as much, usually I use more common ones.

About the rest, septum purge flow and influence of the variation of the split ratio on the area, I have to check with the engineer as he was the ones performing the trials.

Thanks

[rp18]

I already thought it was Shimadzu...

Shimadzu has a very common problem also described in the manual. If it's the usual split/splitless injektor it's possible that the septum touches the removable (hot) metal part (I don't have the exact name for it, I have the German manual) under it causing bleed. You may have to remove some graphite from the liner seal so that this part gets deeper into the injector and doesn't touch the septum any more. It is described somewhere in the manual.

Hope this was it.

[pollypocket78]

Oh! really? I will have a look at the manual! Can you tell me where it is exactly in the manual? The chapter?

It would help me a lot, thank you so much!

[rp18]

I have an older model (GC14), but the injector has pretty much the same layout in the 2010 as far as I know. In the injector chapter of my (old) manual there's a part on how to fit the graphite ferrule for the liner. There should also be a special tool for it (forming jig).

[pollypocket78]

Ok thanks I will have a look and tell you afterwards...

[pollypocket78]

I had a look at the injector port description of the manual. The ferrule you're talking about is it before the injection chamber or is it after? The only ferrule I can see is right after the capillary nut linked to the column, which is after the injection vaporization chamber.

I can't really see what is to be changed or fix, and how can it be possible that the contamination happened as I only changed the septum?

In my manual, the troubleshooting part, I can't see anything relevant about this pb of ferrule. Maybe, as it is a very recent model from last year, they don't explain it anymore in the manual



Thanks for your time and help btw!!

[rp18]

It's the ferrule IN the injector, the one that's around the liner.
I hope it's the same design in the 2010...

If you press the new septum to deep it may touch hot metal causing the bleed. Running the GC at low temperature (< 80°C) for a while before starting the usual gradient should increase the peak. Increasing the septum purge flow should lower it.

EDIT: I took a look at my colleagues lab with a 2010 and it seems the injector liner now has an O-ring instead of the graphite fitting. However, the septum can still be the cause for ghost peaks. Measure septum purge flow and don't over-tighten the septum nut.

[macgyver]

Here's a few ideas:

Make sure you use the green septa (Supelco Thermogreen LB2) and not the white ones. Shimadzu changed to the green ones when they released the QP-2010 Plus, but still use the white ones on GC-2010, so some labs have both lying around. The green ones don't bleed as much.

Replace the liner o-ring. The QP-2010 Plus and earlier model QP-2010 don't used graphite ferrules on the liner.

Take the capillary adapter off the bottom of the injector and make sure there are no particles of septum sitting in the bottom of the injector. When you reattach the capillary adapter, you should probably fit a new gold seal between the capillary adapter and the injector base if it doesn't have one.

Cut a short length off the column and reinstall with a new ferrule.

Give the system a good bakeout (>250 deg - check your maximum column temperature first).

[Balderquell]

I've seen phthalates bleeding out of bad o-rings and septa.

What's injector temp?

Beyond the thermogreen septa there are the "orange" variety which are stable up to 450C. Might try those. You can also try graphite liner o-rings.

Phthalates are ubiquitous though. Do you see the contamination in a dry-run of the instrument? If not, then it's your sample/standard preparation.

Eliminate all contact with flexible plastics during extraction or preparation for analysis. No latex gloves, plastic disposable pipets, you name it. Check the solvent grade. ACS grade can often have trace levels of phthalate. Improve the extraction glassware cleaning procedure.

[pollypocket78]

Thanks a lot for your messages.

rp18, Indeed the 2010 plus does not have anymore ferrule in the injector, but an O-ring. This one has been changed as well during our multiple trials.

We are going to try something else with an other type of septum today. Balderquell, a dry run of the instrument is the same. We ran a lot of non injection runs with/without the syringe with/without solvents.

About our solvent I am trying to change the analytes regularly to be sure it's not where the contamination comes from. And just before the maintenance I did that sdtarted all these pbs, it was the same solvent/analyte and there was no peak.

Mac Gyver, I will try to see the bottom part of the injector unscrewing my capillary column and checking it.

Will keep you update!

Cheers everybody!