Len
I would look for a couple of things. First, I would try and figure out
whether the noise is detector-related or spray-related.
If you turn off the spray voltage (leave the instrument on, set the spray
voltage to zero, turn the liquid flow off), and you still see the same
spikes, then the noise may be coming from your detector. It could be a
noisy dynode or multiplier. A simple cleaning or dusting off of the dynode
with a gentle clean flow of inert gas will often fix the problem. All it
takes is a few specs of dust to make a noisy dynode.
If the noise goes away when you turn off the spray, then the detector is
probably ok. Then, the noise is likely related to the spray. This is a
phenomenon I like to call "mudball noise". Large droplets which enter the
system and are not effectively desolvated can cause these noise spikes. The
heated capillary is off-axis relative to the skimmer, so that should get rid
of the big "mudballs". I have seen cases where the heated capillary end
(the portion inside the vacuum) gets bent so that it is not as much off axis
as it should be. This could give you increased noise. You might also try
moving the nanospray tip back or at an angle. I know there are some that
like to operate with the nano spray tip inside of the heated capillary
entrance, but I think that causes more noise than the extra gain in signal.
Regards,
Mark Hail
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-----Original Message-----
From: Association of Biomolecular Resource Facilities
[mailto:abrf-request@aecom.yu.edu]On Behalf Of Len Packman
Sent: Thursday, November 30, 2000 10:15 AM
To: Recipients of ABRF List
Subject: nanospray LCQ Classic
Dear LCQ users
In nanospray (Protana) of C8-cleaned-up in-gel digests, spraying at
0.7kV in 0.2%formic/70% MeOH I frequently see random spikes in
profile mode (largely filtered out in centroid). By collecting a
number of scans and averaging, the spikes don't really affect the
data quality but I wonder if anyone else has seen this and knows the
cause of such annoying features.
Len
-- ********************************************************************* Dr Len C. Packman Assistant Director of Research Department of Biochemistry University of Cambridge 80 Tennis Court Road Cambridge, CB2 1GA, UKTel: +44 (1223) 333639 FAX: +44 (1223) 766002 e-mail: l.c.packman@bioc.cam.ac.uk
Protein and Nucleic Acid Chemistry Facility http://www.bio.cam.ac.uk/proj/adr/PNAC/pnac.html
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