There is a program called IsoPro that calculates mass distributions. It
will take a formula or amino acid sequence as input, and it has options you
can set to determine what the simulation looks like. It's at
<http://members.aol.com/msmssoft/>, as well as a similar program, FragPro.
David Bostwick
School of Chemistry and Biochemistry
Ga. Inst. of Technology
Atlanta. GA 30332-0400