Re: DNA MALDI prep

Lina Shebaro Germann (lsgermann@maldi.com)
Tue, 20 Jul 1999 09:07:37 -0600

the Na adducts you see is normal when your sample is not completely "clean".
when I say sample, I mean both the matrix and the analyte. they both have to
be free of Na salt. The use of Ammonium salts helps because NH4+ doesn't
form much of adducts, but it is not enough if you original sample is full
with Na+. sodium salts come from matrix, glassware, water that is not
completely ultrapure, oligo that has not been HPLC purified, etc...
there are few methods of how to get rid of Na+. One method using cation
exchange resin beads, described in one of our application notes (Application
note
#3) on our webside (www.maldi.com). Feel free to check it out. You can
download it or I can send you a copy if you need one. another method is
using NAP 5 Columns (Sephadex G-25 Medium, DNA Grade) from Pharmacia
Biotech. you pass the oligo solution through the column and it gets rid of
some of the sodium salt.

Let me know if you have any more questions about this subject.

Good luck.

Lina Shebaro Germann, Ph.D.
Maldi Application Chemist
BioMolecular Instruments
A Division of Thermo BioAnalysis
504 Airport Rd., Santa Fe, NM 87505
phone # (505)471-6124 ext. 241
fax # (505)474-5203
www.biomolecular1.com

----- Original Message -----
From: Michael D Knierman <KNIERMAN_MICHAEL_D@Lilly.Com>
To: Recipients of ABRF List <abrf@aecom.yu.edu>
Sent: Monday, July 19, 1999 3:26 PM
Subject: DNA MALDI prep

>
>
> Dear MALDI colleagues,
>
> I have a question concerning the sample preparation of DNA for MALDI
analysis.
> Why are users including an ammonium salt? I have used 3-hydroxy picolinic
> acid with ammonium tartrate and have a good spectra that matches the
expected
> mass of the analyte, but there is a huge amount of adducts in the
spectrum.
> The mass of the main peak matches the expected mass not the mass + NH4, so
why
> the ammonium salt? Most of the adducts were +22 (Na). Before I go off
and
> investigate how to get rid of the adducts, all comments would be
appreciated.
>
> Mike Knierman
> Eli Lilly
>
>
>