Hi all, I am a novice in the practical aspects of GC (most of my background/knowledge is LC) so I realize this is a very basic question. After determining impurities in my samples were due to vial cap septum bleed, I was hoping to get some feedback on the following topics: Should vial caps be used for multiple injections in the same batch (i.e. blank injections)? If vials/ samples are reused, is it common practice to replace the caps after single use? Or can they be used again within a short time period (i.e. same day)? Is there a recommended vial septum material for ACN solvent? I know Agilent recommends rubber/butyl but I have seen conflicting information elsewhere (perhaps just difference in manufacturing?). I appreciate any and all help/ tips for a GC novice. Thanks, Brian

There is a white paper from Agilent on septum/solvent compatibility: https://www.agilent.com/cs/library/whitepaper/Public/5991-6770EN.pdf From experience and with dichloromethane (DCM) as solvent, caps are for single injection. Recapping has been (mostly) successful only right after the injection has been made. I really try to keep plastics away from DCM during sample prep because of its stripping effect.

Recommended # of injections per vial cap/septum?

bguo23 over 3 years ago

Hi all,

I am a novice in the practical aspects of GC (most of my background/knowledge is LC) so I realize this is a very basic question. After determining impurities in my samples were due to vial cap septum bleed, I was hoping to get some feedback on the following topics:

Should vial caps be used for multiple injections in the same batch (i.e. blank injections)?
If vials/ samples are reused, is it common practice to replace the caps after single use? Or can they be used again within a short time period (i.e. same day)?
Is there a recommended vial septum material for ACN solvent? I know Agilent recommends rubber/butyl but I have seen conflicting information elsewhere (perhaps just difference in manufacturing?).

I appreciate any and all help/ tips for a GC novice.

Thanks,

Brian

Top Replies

csiquet_flex2000 over 3 years ago +3 verified

There is a white paper from Agilent on septum/solvent compatibility: https://www.agilent.com/cs/library/whitepaper/Public/5991-6770EN.pdf From experience and with dichloromethane (DCM) as solvent, caps…

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0 Rwilson over 3 years ago

Hi Brian,

What kind of detector are you using? From my experience with FID, you shouldn’t have issues with septa bleed from re-running samples within the same day. If you inject the vial and then re-run it after a day, you will probably see n-hydrocarbon peaks related to septum bleed. Now this is with a FID, it may be more severe with GC-MS. Also, if you are using septa in your inlet, you’ll want to change that out about every 100 injections.
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0 Rwilson over 3 years ago

Hi Brian,

What kind of detector are you using? From my experience with FID, you shouldn’t have issues with septa bleed from re-running samples within the same day. If you inject the vial and then re-run it after a day, you will probably see n-hydrocarbon peaks related to septum bleed. Now this is with a FID, it may be more severe with GC-MS. Also, if you are using septa in your inlet, you’ll want to change that out about every 100 injections.
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0 wcody over 3 years ago in reply to Rwilson

To add to what Rwilson contributed, don't forget about the sample wash and solvent wash vials. Those septas will also need replacing or can contribute to septum bleed contamination.

Below are links to two great resources for general good practice.

Better Connections, Better Results with Your Agilent GC System

Don't Fear the Ghost or Unexpected Peaks: Troubleshooting and Prevention
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0 bguo23 over 3 years ago in reply to Rwilson

We're using GC/MS so more sensitive. Thanks for the inlet septa note! It is probably due for a change.
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0 bguo23 over 3 years ago in reply to wcody

Thanks for the link! I ordered replacement wash vial septa. I'm taking over management of the instrument from previous employees but I suspect they did not maintain that well.
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0 wcody over 3 years ago in reply to bguo23

Happy to help.

With any future ghost peak troubleshooting you do, keep this in mind about septa contamination, if it is a peak it is likely being introduced at injection and going through chromatography on the column. If it is a constant background contamination of certain masses, such as showing up even in a tune, it is septa material in the system.

By removing the syringe and performing an injection, you will have a quick test to see if the contamination is in the system or coming from something the syringe is either passing through or pulling solution from.

Don't over tighten the septa cap. Replace septa on the inlet, wash vials, and change the liner on a regular basis and you will likely eliminate most of your septa contamination problems.
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0 garyb014 over 3 years ago in reply to bguo23

Our wash vials don't have septa we have these inserts, Agilent part 07673-40180.
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0 bguo23 over 3 years ago in reply to garyb014

Right, that's what I ordered. Just habit to call all vial cap liners 'septa'
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