the sodium adducts are exactly the reason for the addition of the ammonium
salts. If you have sodium or potassium ions in your solution you will get
an extensive adduct formation with nearly no visible amounts of the [M-H]-
ion. The reason for the ammonium addition is to force the oligo to form
ammonium adducts and not alkali adducts because ammonium adducts will decay
into ammonia and the molecular ion and are therefore normally not visible
in the spectrum. What you see should be the [M-H]- ion.
If you still observe alkali adducts despite the addition of ammonium
tartrate (or ammonium acetate, which I use), you should try to clean up
your samples with cation exchange resins like Amberlite CG-120 (using the
ammonium or hydrogen form!).
Yours sincerely,
Marcus Macht
**************************************************************************
Dr. Marcus Macht
University of Cologne
Centre for molecular medicine - Service laboratory
Joseph-Stelzmann-Str. 52
50931 Cologne, Germany
Tel.: +49 221 478-6995
Fax: +49 221 478-6977
e-mail: Marcus.Macht@uni-koeln.de
**************************************************************************