Sequence Analysis of Polypeptides by Direct Chemical Ionization Mass Spectrometry

Abstract

The identification and structural elucidation of small, biologically active peptides is a challenging analytical problem. These compounds are often not amenable to classical protein sequencing methods because of the presence of N-terminal blocking groups, carbohydrate side chains, or covalently modified amino acids. The low volatility and thermal lability of most polypeptides requires that they be derivatized prior to conventional electron impact (EI) or chemical ionization (CI) mass spectrometry for complete structural evaluation (1). Unfortunately, peptides of biological origin are often obtainable only in sub-nanomole amounts which makes sample consuming derivatization highly undesirable. Furthermore, chemical treatment may modify or destroy sensitive functional groups present in the peptide.