David H. Singleton
Scientist
Pfizer Central Research
PO Box 8003
Eastern Point Road
Groton, CT 06340-8003
-----Original Message-----
From: Jim.Bloom.B@bayer.com [mailto:Jim.Bloom.B@bayer.com]
Sent: Thursday, February 25, 1999 10:34 AM
To: Recipients of ABRF List
Subject: MALDI-TOF vs ESI-MS
Good morning all, I have a question for the MS guru's. We received two
peptides from a client with calculated masses of 3950 and 4950 (the
peptides,
not the client). When I put these peptides in my trusty 6 year old single
quad
ESI-MS, I saw very pretty envelopes and obtained the desired masses. My
colleague, who has learned how to run a new MALDI-TOF MS that we have access
to, was anxious to show how superior the MALDI is and basically to prove,
once
again, that I am just an old fogy. Unfortunately, I have had to admit that
her
"toy" is more sensitive than mine but I also like to point out that I rarely
if
ever have to calibrate "my baby" while she has to calibrate every time she
fires up the machine. I digress. So, for the 3950 peptide she got a nice
peak
with the correct mass and gathered at the foot of the peak were other masses
that presumably represent adducts of some sort including one that is 17 amu
smaller than the major peak. The 4950 peptide didn't appear to "fly" as
well
(or she was unable to find a good 'sweet spot' ...note one does not have to
hunt around for a 'sweet' spot with my trusty old single quad!!) and there
were
two major peaks of equal intensity, one with the correct mass and the second
with a mass that is 17 amu smaller. Now, in the case of the 4950 peptide,
if
we had run only MALDI-TOF MS, we would have told our client that he had the
correct peptide plus an "incorrect" form of the peptide...you name it,
pyroglu,
one of several amino acid substitutions or whatever else one can find in
DeltaMass. My trusty old single quad tells me that our client has the
correct
peptide and it is pure and the MALDI had generated a -17 artifact. So, to
put
my young whippersnapper colleague in place, could someone tell me that, yes
indeed, the MALDI has produced an artifact and maybe tell us what most
likely
the artifact is (has the MALDI knocked off an -OH??) and perhaps most
importantly, how to prevent the machine from producing said artifacts!! I
would be most grateful!!
PS: In case it is important, the MALDI-TOF was run in positive ion
reflector
mode with delayed extraction.
Weather inconsequential: Spring has arrived, pink blossoms on trees that
produce pink blossoms and grass needs to be cut!!
Jim Bloom
Bayer Corp.
Berkeley