Dear Bill,
in my experience, DHB has no real MW cut-off, at least not in the range you
mentioned (I could already acquire negative mode spectra of 7
kDa-oligonucleotides), but at a first glance it seems to be the matrix of
choice for this type of molecule.
>From my point of view, there are two things you can try. First: Yes, you
should expect severe adduct formation caused by the glycan moieties. This
will be primarily sodium and potassium. You can try either treating the
sample with cation exchange resin or adding some alkali ions (e.g. KOAc).
Hopefully this will bring your molecules either in the fully protonated
form or in the fully "alkaliated" form and result in single signals for
each oligomer.
Second: You don't write anything about your hardware, but at our Bruker
MALDI it is possible to cut off the low MW part of the spectrum either by
deflection of the fast moving ions or by gating the detector. This should
be possible at most commercial instruments. Disabling the saturation of the
detector (with matrix signal etc.) will usually lead to a dramatic increase
of sensitivity in the higher m/z region.
I hope this helps.
Yours sincerely,
Marcus Macht
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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
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