Chromatography Forum

I have been running GC/MS for over 3 years but am new to running splitless. Currently I am using straight liners packed with glass wool in the middle. I am having troubles with gigantic peaks coming out after the solvent front should be alluting and drowning out some of my analytes. I am also finding that when I am changing liners, the glass wool ends up right at the top of the liner (right below the septum, basically), rather than in the middle where they start out (when I install them). I am still trying to figure all this out. Does this mean anything to anyone else?

Thanks.

I have been running GC/MS for over 3 years but am new to running splitless. Currently I am using straight liners packed with glass wool in the middle. I am having troubles with gigantic peaks coming out after the solvent front should be alluting and drowning out some of my analytes. I am also finding that when I am changing liners, the glass wool ends up right at the top of the liner (right below the septum, basically), rather than in the middle where they start out (when I install them). I am still trying to figure all this out. Does this mean anything to anyone else?

Thanks.

Well could be some other issues with regard to the giant peak, but you have not posted any details on what you run and how the instrument is set up.

As for you choice of liner: Not good, for splitless I use a tapered liner (narrow at bottom or double tapered narrow at bottom/top), secondly I tend to use "focused" liners ie they are made so that the prepacked wool stays in place especially for splitless injections.
There reason for the wool moving around could be that you pack too little if it alternatively too much so the syringe gets "stuck" in it and pulls it upwards.

The wool issue is of course one possible reason for the "giant" peak issue.

Also I would typically turn on the split perhaps 2min or so depending on settings after each injection to "clear" the injector.

Using a straight liner in splitless may led to that the evaporated sample escapes from the liner and enters the injection port area and in worst case the gaslines.

Please post more details so we better can help you.

btw happy holidays, I am off work until 7th of January

I have found (by accident) that if you don't turn off the column flow before changing liners, the glass wool will be blown to the top by the pressure in the inj port/column when you remove the septum. I would also recommend changing to a tapered liner.

I run derivatized plant samples and standards.

Details: It is an agilent 7890gc/5975ms. Helium is carrier gas. The solvent we use (mostly) is Pyridine. I run splitless with 1ml/minute column flow. The septum purge is set up to open after 2 minutes. Inj. port temperature is 250C. I am not certain what other details might be useful.

I am planning to switch to tapered bottom liners. Right now we are running straight liners pre-packed with glass wool in the middle because that is all I have access to. Once the new liners come I will be switching. I am considering doing away with the wool, though that might damage the column more quickly.

Thanks in advance.

Hi esloomis!
In my experience using split liners for splitless injection does not work well. Anyway, Agilent’s single tapered liners work fine for split and splitless.
Some other tips:
· when injecting in splitess use a oven temperature slightly above your solvent’s boiling point (10ºC or so) and hold it about 2 minutes. Allow enough time for your solvent to elute from the column. Those 2 minutes should take care of it, if not, increase the isothermic time.
· I regularly work in splitless, I use single tapered liners from Agilent (I work with two 6890s) and pack myself the glass wool. Just a whiff about the middle of the liner to whip clean the needle and trap the non volatile junk.
· For your samples (e.g. plant extracts) which seem to be “dirtyâ€