I am not familiar with the ion your a looking at but one guess to the
origin of the ion is that -88 is the -97 metastable ion that is formed in
the drift tube. One easy way to check is to run in PSD mode and select on
[M+H]+. If the -88 is still there and the -97 is gone then -88 is most
likely the -97 metastable. To be certain, you would have to run PSD and
calibrate to determine the mass of the fragment. This is a common
observation when a fragment molecule is ionized in the source and when the
fragment ion is produced from unimolecular decay in the drift tube in the
same acquisition.
Regards,
Damon.
At 02:08 PM 10/20/98 -0400, you wrote:
>We have noticed that since installing delayed extraction on our MALDI-Tof
>instrument, reflectron analyses of phosphoserine and phosphothreonine
>containing synthetic peptides give a low amount of the characteristic -97
>dalton ion, with a more predominant peak at -88.3 to -88.9 daltons. Have
>others seen this latter ion as well and does anyone have an explanation for
>its origin?
>
>Thanks,
>
>Kathy Stone/Ken Williams
>
>
Damon C. Barbacci
The Laboratory for Biological Mass Spectrometry
Department of Chemistry - MS 3255
Texas A&M University
College Station, TX 77843