Chromatography Forum

Hi all,

I've got a problem with our Agilent 7890 GC/MS headspace system regarding a persistant contaminant peak which is co-eluting with a peak of interest - but according to the scan the peak of interest (in this case ethanol) is not the contaminant.

It has a consistent RT which led me to believe that it could be an injection problem so i have investigated the following:

- Replace septum/liner: NO EFFECT
- Replace Syringe: NO EFFECT

So i decided to turn my attentions on the column:

-Baked the column as described by Agilent: NO EFFECT
-Trimmed the column: NO EFFECT
-Even installed a new column: NO EFFECT

I am currently checking the vials being used are not causing the problem but i feel that i am scraping the bottle of the barrel now.

Have i missed something?

Any opinions would be welcome.

Thanks

Steve

Is this liquid injection? If so, what are you rinsing the syringe with?

Is the peak present if you run the program without an injection?

Its a headspace injection for analysing solvent levels.

Since my previous post i have rigged up the system to inject using the back inlet and have found this cures the problem. But, this means that i must have a contamination in my front inlet which is not inluenced by the syringe, liner or septa.

An analyst introduced air into the system recently whilst changing the supply cylinder. Is it plausible for the contaminant to be linked to this? This problem started after the cylinder change but not immediatley after.

I have very limited experience with the MS system but if purity of carrier gas is an issue, could the contamination be in the air pipe feeding the front inlet?

Going back to Consumer Product Guy's questions: If you can get the peak from a blank injection, the spectrum could help to identify the interference - and may indicate the source.

sorry, the peak is present in blanks too. Same RT and roughly same area.

I have ran the peak through the library but it isnt coming up with anything concrete - figures are around 1-4% confidence.

There is very little information to go on here, what are the prominent ions in the contaminant?

wrighty,

Splitless or split injection? If split, what is the split ratio? If splitless, how long and carrier flow? When was the last time the split vent line or trap was changed?

Best regards.