[Protein-analysis] multiple MS peaks

[Anna]

Hello,
   
  I recently purified a small recombinant protein (~3,000Da).  Mass spec analysis showed me four peaks one (the smallest) was the expected size and the others were 32, 64 and 128 Da smaller than my expected protein size.  I was wondering if anyone could suggest an explanation for this loss in mass?
  Thank you in advance,
  Anna

 
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