multiple antigenic peptides - MALDI

[John E. Fox]

We synthesise custom multiple antigenic peptides, (octomeric peptides) according to 
the method of James Tamm, Immunol Methods (1989) 124, 53-61.
As part of our quality control checks, we have tried to analyse them on a MALDI mass 
spec. using gentisic acid as the matrix. 
We see no sensible spectrum at all for any of the peptides we have made. 
These peptides have molecular wieghts roughly in the range of 10KDa to 18KDa, 
so they are well within the working range of our machine, (a Kratos MALDI 3).
We have tried them on another machine with exactly the same results.

Has anyone  else tried to mass spec these compounds? Anyone with an idea of why
we have failed to see their spectra?