getting oligo spectrums on mass spectroscopy

Hello all,

I'm just received a mass spectrometer at work and can't seem to get a
decent spectrum of  a 20 mer oligo.  I have been setting my laser
intensity between 1700 and 2200.   When I do get peaks at 6117g/mol
they have an intensity of 500 or less.  Is this background/noise or
possibly the sample?

I have varied the concentration of the sample from 100ul of HPLC water
to 500uL of water then spotted the plate with 1.5uL.  I know the
sample should contain either a 19mer or a 20mer because of the results
run on the HPLC.

Extra information: running oligos with 40nm columns, using 1mL
ammonium hydroxide to cleave then heating for 1 hour at 95C.
Any advice would be much appreciated. 
Thanks.