RE: MALDI-TOF Ion supression

LANGE, GARY W [PHR/1005] (GARY.W.LANGE@stl.monsanto.com)
Tue, 7 Dec 1999 10:47:35 -0600

Micheal Knierman's reference is a good one to consider. I think the paper
by Cohen and Chait (Analytical Chem 1996 68 31-37) is also food for thought.
Different pH's with the SAME matrix will acentuate different peptides in a
mixture. Different drying conditions and large or small crystals will also
influence which peptides are more easily seen. I think something else to
consider in the suppression of peptide mixtures is the buffer, strength and
type that you have present. More junk will always produce lower total
signal. Consider 5-10 mM buffer instead of 50 mM unless you are planning to
ziptip. If you mix ammonium bicarbonate with TFA then you will produce TFA
ammonium salts which has been said to repress signal, when compared to low
mM Trisma digests. (Electrophoresis, ~ March 1997 Guang Li et al). I think
that the TFA salts may inhibit some ions more than others too. If it's
important to get as many peptides as possible then using a ziptip might be
the best way to go. Just slowly increase the acetonitrile/TFA
concentrations so that you effectively separate most of the smaller peptides
from the larger and more hydrophobic peptides. 10% 40% and 80% ACN
concentrations work pretty well for rough separations. Don't forget to
rerun the plate in the negative mode either as some of those supressed ions
will pop up.

Gary Lange
g.w.lange@monsanto.com
636-737-6602

-----Original Message-----
From: Brett Phinney [mailto:phinney@unity.ncsu.edu]
Sent: Monday, December 06, 1999 11:15 AM
To: Recipients of ABRF List
Subject: MALDI-TOF Ion supression

I am trying to find a good reference that explains and documents the ion
suppression phenomena seen when analyzing complex mixtures such as peptides
by MALDI. Does anyone know of such a reference?


Thanks a lot


Brett Phinney
Department of Biochemistry
North Carolina State University