I don't understand your problem - are you saying you are seeing peaks but not the peaks you want (ie monomeric peaks)? Or are you not seeing any peaks at all?

If you are seeing multimeric peaks then in addition to adding DDT perhaps try diluting your sample. Aggregation will be promoted at high concentrations.

Thanks Charles...

I am getting multiple peaks, somewhat like hedgehog peaks. Among them, the intensity of peak with monomeric mass is very less. I will try diluting the sample too.

Can you post some examples of your spectra along with the individual experimental conditions?

Does your peptide contain Cys ?

This may work:

1. Dissolve a very small amount of peptide in HFIP and evaporate the solvent.

2. Treat with a reducing agent like DTT or beta-mercaptoethanol in water.

3. Add TFA to bring the pH to 2 and de-salt using 0.1% TFA in acetonitrile.