question - (Nov/05/2008 )

. A researcher is making a synthetic peptide in order to use it as a calibration standard for mass spectrometry. The theoretical monoisotopic molecular weight is 2464.19 Da (where the sequence corresponds to: RPVKVYPNGAEDESAEAFPLEF). For quality control purposes he decides to check the mass by performing electrospray ionisation mass spectrometry in positive ion mode. The mass spectrum shows two peaks that correspond to m/z = 1233.095 Da and m/z = 822.397 Da. Has there been a failure of synthesis? Explain the measured masses?

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