Agilent 1100 MSD (1946B) baseline noise

[chrsdrake]

Help please, I am quite new to MS and have a problem that is way beyond me.

We have an agilent 1100 LC system with a single quad MSD detector - model number 1946B. We are using the system to analyse the tannins in plant extracts, so the MS is used in TIC mode to give us the mass of the eluting uv peaks.

The system was shut down over the xmas break and after restarting we have a very noisy MS baseline.


This is a typical result before xmas, uv at 280nm (above) and TIC negative below.


And here is a similar sample run (using the same LC/MS method) after xmas.


Does this look like contamination or an electronic problem or something else. I can provide details of LC and MS parameters but dont really know which of these will help.

Note, the problem is the same in positive mode.

Thanks

Chris

[mckrause]

Can't see your chromatograms, but we have seen something very similar to this on our 1946D. I broke it down and cleaned EVERYTHING, and then very carefully adjusted the ESI capillary after a small trim. It improved a lot. Check your rough pump vacuum; it makes a really big difference for some unknown reason.

[chrsdrake]

Yes sorry I seem to have messed up inserting the chromatograms. I did manage to trace the problem to poor nebulisation/evaporation so the "noise" I was seeing was caused by droplets getting into the system.

Chris