Although I lack the experience, I can relate my understanding of the
situation regarding the Micromass Qtof. A parent "scan" on a qtof is simply a
series of daughter acquisitions (apologies to those who feel that equating CID
fragment ions with girls, or that parents might give rise to girls, is sexist),
since that is all the qtof can do. You need software upfront where you can
specify that you want to acquire a daughter acquisition for a few seconds at a
parent m/z of, say, 400, then another one at 401, 402, and so on up to m/z 1000.
In this example, you then have 600 daughter scans acquired over 10 minutes, and
the data can be viewed in the same way that an LC/MS/MS file can be viewed. So
you could look for any scan that might give rise to a particular daughter ion,
say m/z 86, to find the parent ion that might be due to a peptide producing a
Leu/Ile immonium ion. I think the Micromass software might also let you locate
daughter acquisitions that contain ions at a m/z higher than the parent, which
would allow you to find the multiply-charged ions in the "parent scan" . As you
can imagine, these "parent scans" are quite slow and are suitable for nanospray
experiments where you have enough time (a few minutes), and I don't see how
these "scans" could be implemented for use with LC/MS where the individual
components elute within a few seconds.
Apparently there is a minor hardware change that can be made to the
Micromass Qtof that speeds the process up some. Rather than stepping at one m/z
unit at a time, it drops the resolution of the Q in the Qtof to pass 50 m/z wide
windows. If there are any interesting ions (m/z 86, or fragment ions at a m/z
greater than the parent window), then the resolution is decreased until the Q
homes in on the particular parent that gave rise to the interesting fragment.
If the wide parent window passed no ions that gave interesting fragments it
steps up to the next 50 m/z window. I don't know how quickly these can be done.
We have a triple quad, which we would use if we wish to obtain parent scans.
Rich Johnson
"alex bell" <ehjb@musica.mcgill.ca> on 09/24/99 04:49:21 PM
To: Recipients of ABRF List <abrf@aecom.yu.edu>
cc: (bcc: Richard S. Johnson/ProteinChemistry/Immunex)
Subject: Re: MS (parent scans)
Dear all,
There seems to be a lot of confusion regarding quadrupole(sic)ToF MS and parent
scans.
I am with the belief/misconception that it is both the software up front and for
data analysis that is CRUCIAL for allowing one to set-up and/or extract the
relevant results form a QToF MS/MS experiment.
Could we get some feedback from experienced scientists.
Best regards,
alex
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