Chromatography Forum

I'm trying to analyse a sample with a chloroform matrix but it keeps melting the BTO septum after only one or two injections.

Can anyone suggest a septum which is resistant to chloroform at ~260C?

Cheers

Interesting problem - if the GC inlet is working as it should the solvent should never get anywhere near the septum. What hardware do you have ?

Peter

Septa BTO, a Thermo/Fisons GC ?
If you are running Chloroform , why do you have the injector at 260C ?

I doubt that your Chloroform is attacking the septa, I think the septa is being exposed to too much heat. Although rated higher BTO septa commonly melt onto hot injectors. The Thermo SSL one is most prone as it is heated to ensure that the top of the injector will be the same temperature as the middle and the bottom. Great for good sample transfer bad for septa. Re your method , what are you analysing and why 260C. How high does your column ramp go ? With the Thermo SSL you should not need to exced the max column temperature on the injector and if that is only for a column clean you may not need to even have it so high

Humm, thanks for your thoughts guys but the chloroform is indeed attacking the Septum - just the residual solvent on the syringe surface is enough to begin the melting process. It's a Thermo setup. 260C is nowhere near the operating limits of a BTO septum (I regularly use them up to 400C without problems). I'm not aware of a non-silicone septa for GC but wondered if anyone else had come across a chloroform-friendly stopper anywhere?

If residual solvent on the needle is really the problem then a work around may be to programme a pause into the autoinjector so that the needle gets a chance to dry off between picking up sample and injecting.

Peter

I used to do many injections with chloroform as a solvent (years ago - so I dont remember the septum). This was with an autosampler. I suspect any problem with liquid on the outside of the syringe would have been taken care of by the GC vial cap wiping the needle as the syringe was withdrawn.

If you are not using an autosampler, I would suggest injecions from capped vials - it also contains the chloroform in the vial, reducing exposure for the operator.

If you are using an autosamler, I am puzzeled that you would have any significant quantity of liquid on the outside of the needle.

Simple really, vials are not covered as the chloroform melts the cap septa as readily as the inlet septum and then introduces a forest of siloxanes into the sample. (Silicon based compounds are part of the analysis)

The idea of an injection lag is a good one, so thanks for that I'll check it out.

Hi Wheeltops

Have a look at the septum compatabilities for headspace vials - -I recall that there were specific materials for chlorinated hydrocarbons, but not exactly what they were

Peter

How about diluting the samples 10x in another solvent, such as methylene chloride before injecting to GC?

Having done many samples in chloroform with capped GC vials, next question: could it be your analyte? I have seen things like acid anhydrides attack silicone septa.

Other thought - give your favorite GC consumables supplier a call. Talk to an applicaions support person. They know the current product line - and since chloroform is not that exotic a solvent, they should be able to give a very good answer.

Thanks - I may just try it...........

wheeltops,

There are teflon coated (layered really) vial septum that are available. These should allow you to seal the vials. The GC septum, that is another story since you will be doing multiple injections there. Have you considered a Merlin Microseal?

Best regards,

AICMM

Vial kit from fisher:
03-391-15
vials with screw on caps with septa...never had any problems, I think they have a layer of teflon and silicone