Agilent GCMS 7890A with 5975C Problems

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

7 posts Page 1 of 1
We are having many problems with our GCMS lately. It was recently sent off for repair due to a fault with the sideboard. This was then replaced (part number G3170-65015) and since getting the system back the results we have been obtaining are terrible.

Some compounds aren't visible at all, we just get a noisy baseline. Some compounds do have peaks with corresponding masses but the peaks are very wide with heavy tailing. Only one compound of the ~20 references I tested came out with a nice sharp defined peak.

The method I am using is the same as prior to the repair and the same as used by another lab with their GCMS (they get nice defined peaks with the same compounds).

I am noticing a slight pattern (needs further testing to prove though) but I think the lower boiling point compounds we test generally have better peak shapes than the higher boiling point compounds.

Could it be that the interface is not heating correctly and the higher boiling compounds we test condense and don't make it to the MS?

Alternatively, perhaps our column degraded whilst the MS went off for repair. I don't know if the column was plugged whilst it was disconnected.

The system passes the tune program fine, there are no major leaks.

Any input would be appreciated. If necessary I can post the method but I really don't think that is the issue.

If you can get a good tune, but bad results while injecting, it sounds like the problem is indeed at the GC side.

Lower boiling point compounds being less affected by your issue is, unfortunately, not very helpful in narrowing down where you need to look. A degraded column, a dirty inlet / liner, an interface that is not heating, .. will all affect heavier compounds more than lighter ones.

I suggest to do the usual GC maintenance first (inlet cleaning, new liner/septum, trim inlet part of column,...), and if that doesn't help, replace the column.
Thanks for your input. We already cut off 15cm from the column, replaced the gold seal, septum, liner etc. Didn't change anything.

I will replace the column with an old one we have this week. If that fails, I'll buy a new column.

Will report back :)
Does the source temperature read correctly? Or at least heat up and show a change from ambient to whatever temperature you set it to? (Normally around 250C)

Also it the interface is hot you will know it because the nut on the inlet at the column will be hot. If the interface is set to 250C you should be able to put a drop of methanol on the interface nut and see it instantly boil away or find some way to measure the temperature. Touching it works but can be painful so I try to avoid that, it happens enough when I do inlet maintenance.
The past is there to guide us into the future, not to dwell in.
Yes the source is OK. I touched the nut and it was pretty damn hot so that is also fine!

I changed the column today and I am at least seeing my peak now so that is a relief. I've got a raising baseline though so I think column bleed. I will buy a new column anyway.
While waiting for a new column, you could bake out the old one for a couple of hours, or overnight, to try and get rid of the baseline increase.

James_Ball wrote:
Touching it works but can be painful so I try to avoid that, it happens enough when I do inlet maintenance.

This is really, really annoying. Especially if you're blessed with large hands :lol:

Send us one picture with the Chromatogram and mass spectra.

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