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Baseline lump
Posted: Fri Jan 25, 2008 4:36 pm
by torduch
Hi,
I’m having trouble with a “lumpâ€
Posted: Fri Jan 25, 2008 5:24 pm
by GOM
You appeared to have changed most things. Have you changed the gold inlet seal? Have you tried a new column?
First try switching off the heater on your injector and allow it to cool down and see if the peak disappears.
Ralph
Posted: Fri Jan 25, 2008 7:16 pm
by chromatographer1
Ralph has given you a good idea to trouble-shoot.
If your GC pneumatics is contaminated (and these things happen) with grease or something that came from the gas line perhaps after a new tank was replaced, then you will see a buildup which will look as you have described.
Does the hump look bigger if you increase your injection port temperature or get smaller if you drop the temperature?
Does the hump look bigger if you increase the time between injections? and smaller if you decrease the time between injections?
These sympthms will occur if the pneumatics are contaminated and will require a complete replacement or cleaning in order to correct the situation.
good luck and best wishes,
Rod
Posted: Fri Jan 25, 2008 11:30 pm
by AICMM
torduch,
What were you shooting before all this happened? I would try a different column, without an injection.
Best regards.
Posted: Mon Jan 28, 2008 5:41 pm
by torduch
Thanks for all the help.
Neither the temperature of the inlet nor the time between injections made a difference on the size of the lump.
I took the weldment off thinking I might as well clean it (since I'm sure its been neither cleaned nor replaced in many years) and pumped some solvent through it - all sorts of junk came out. Unfortunately one of the gas lines snapped off when I was re-installing it, so now I can't do anything until the replacement part comes in.
AICMM -
We've been analyzing coal tar and PAH mixtures. I originally thought dirty samples might be the culprit, but wouldn't the solvent rinses take care of any buildup, since all the coal tar components are soluble in the solvents I used? Unfortunately I don't have another capillary column to try and can't get one for the time being.
Posted: Mon Jan 28, 2008 6:21 pm
by AICMM
torduch,
You reminded me of another area on the 5890 that is subject to contamination. The split vent line will sometimes get gummed up, especially with heavy hydrocarbons. You are already having to replace the weldment, I would suggest removing the split vent line and solvent rinse this (into a beaker so you can see what comes out).
Best regards.