5972 long term issue-any help appreciated

[acrolein]

Hope somebody can help here. I'll try and be brief but specific..

Have a 15 year old HP5972 interfaced with a HP5890 II GC and Tekmar 3100/Solatek 72 concentrator. Here is the problem:

-High baseline, around 40000 counts. It's still there when I direct inject a run and look at the chromatography, so the problem is not Tekmar related.
-Loss of sensitivity and gradual increase in EMV over a week period. I'm currently running a 6:1 split with a Agilent DB624 20m .25mmID 1.12 um thickness column. Purge Valve is constantly "on". Septum purge vent in the front of GC is not capped.
-I do get peaks. The problem seems to be excessive baseline noise which is interfering with some of the compounds, like the ketones.
-MSD was recently refurbed. New motherboard and quads. Problem was evident before this and remained upon completion of refurb
-We had previously split sample through a jet separator and before this problem, had changed over to splitting through injection port. The split vent line was cleaned.
-No "noticable" leaks around system using a helium sniffer.
-Manual tunes look good. Only issue is that over a week period, have to raise the EMV
-Background ions are 41, 55,69, etc. So it has a hydrocarbon 14 amu pattern, although library search tags it as "HAHNFETT". There has not been any stopcock grease added.
-running constant flow (have tried anything from .5-1.0ml/min) and injection port temp is 210, interface temp is 225, source temp reads 145. i have good foreline pressure (33 mTorr) as well.
-Everybody, including an Agilent service engineer is stumped on this one. if you need further info, I can provide it. Thanks for any help offered.

P.S New liner, septa, gold seal installed recently. Column is 4 months old, interface nut is the Restek conversion fitting. I'm "suspicious" of some of the valves in the GC as we hadn't been plumbed to run this way for 14 of the 15 years we've had the system. The sample always ran from the Tekmar transfer line to the column, to the jet, then through a piece of transfer line to the MSD. The injection port was disabled.

[Consumer Products Guy]

You seem to already be trying this this, but I'll emphasize: the issue needs to be isolated whether its MS, GC, or heaspace related. That's the first major step.

[acrolein]

I would tend to think it's GC. The MS has been totally overhauled since this problem started. vacuum pump, tubing, motherboard, diff pump cleaned out and refilled, new quads, source cleaned at least half a dozen times, any traces of apiezon grease around any o-rings wiped off.
As far as the GC goes, the only stuff done to that has been injection port based and the split vent cleaned. All the other tubing, valves and lines in there are original and haven't been touched. Agilent won't support it, in the vein that they won't answer any questions posed via e-mail or phone, and the service rep that came in was on another job in a different part of our lab and came in as a courtesy, but he had no idea as well, but judging by how much work I've done to the MS, I am leaning towards a GC issue.

[Consumer Products Guy]

There are aftermarket service companies that service Agilent 5890 GCs, depending on your location. They are very good systems (I still have 3 in operation, 1 operational one in my warehouse, and a working 5890A in my warehouse that I've saved in case I need parts or its packed-column inlet), but the 5890 series does have some age on them.

I'm not that experienced in how your headspace interfaces, but the GC has traps in its gas inlet plumbing, inside the cabinet on the left side after you remove the panel (yes, you'd need to remove the MSD). There are valves for split/splitless, but they're "after" the inlet, but maybe those are contaminated or leaking. Also, if you have EPC, that could be involved.

[AICMM]

Acrolein,

I don't envy you on this one.... First thing I would do is plug the front end of the column by stuffing it into a piece of septa. Then watch to see if you still have the hydrocarbon background. If yes, vent and cap a short piece of column right in front of the MS with piece of septa. If no, then I would eliminate the injection port as the source. If you could plumb the transfer line from the Tekmar into a 1/16 Swagelok T and the side arm of the T to the back pressure regulator of the HP flow manifold and your problem goes away the problem is in the pneumatics or the injection port. If that does not eliminate it, I would take the Tekmar out of the picture by plumbing the GC direct to the injection port.

Best regards

[acrolein]

Thanks, guys, for all your help on this one. it's definitely a tough one to crack, but I've got some good ideas to go with, so thanks again. I'll let you know what I find.