Chromatography Forum

Hi All,
I have Autosystems and a Varian 3800 GC-MS. On the Varian I was able to use hexane in the WASTE vial of the autosampler. This made sure any droplet of viscous sample from the needle was deposited in the hexane and not taken back up to the bottom of the waste vial septa (to contaminate subsequent sample injections). It worked nicely so long as I wasn't interested in detecting anything eluting near hexane.
However I have the same droplet problem with the Autosystem. Unfortunately I have to monitor the whole "fingerprint" from all sorts of volatile samples.
Is there a completely volatile invisible solvent for GC-FID?
Carbon disulphide looks nasty.
Thanks in advance
WK

Can't help with a less toxic and exact replacement for carbon disulfide in its FID properties and I've been looking for years. However, methods that use it are in jeopardy because the personal exposure limits in air time-weighted over 8-hours are probably reducing from 10 ppm to 1 ppm in many countries. Measuring average CS2 exposure over 8-hours below 1 ppm is no joke either.

HI WK

If your samples are so volatile that hexane co-elutes you probably will not have a problem with carryover, because all the sample will evaporate off the needle during the injection (presuming that you doing hot vaporising injections).

I am not familiar with your uatosampler set-up, but surely there must be some way of rinsing the syringe after an injection or you would get gross caryyover from the residual sample inside the syringe, never mind what was stuck to the outside of the needle.

Peter

Thanks for the replies.
Peter - the droplet forms on the underside of the waste vial septa so the autosampler passes through this vial when other samples further down the sequence are being processed - and this gets deposited either into the next samples or on the outside of the syringe causing carryover.
I will try with lots more sample pumps prior to injection but I think the problem will remain.
Hence I need something to dip the syringe needle into while sample washing.