Gas phase separations of electrosprayed peptide libraries

High-resolution ion mobility spectrometry has been combined with time-of-fl ight mass spectrometry for analysis of a combinatorial peptide library that is expected to contain 676 components. In this approach, the components of a mixture of three residue peptides, having the general form (D)Phe-Xxx-Xx x-CONH2 (where Xxx is randomized over 26 residues including 10 naturally oc curring amino acids and 16 synthetic forms) were ionized by electrospray io nization. Ion mobility/time-of-flight distributions have been recorded for all ions using a nested drift(flight) time technique. The improvement in re solving power [(t/Delta t) = 100-150 for singly charged ions] was illustrat ed by analysis of a mixture of tryptic digest peptides using high- and low- resolution instruments. The approach allows many components of the Library (e.g., structural, sequence, and stereo isomers) that cannot be distinguish ed by mass spectrometry alone to be resolved. Impurities due to side reacti ons appear to be minimal, comprising <10% of the total ion signal. Direct e vidence for similar to 60-70% of the expected peptides is found. Variation in ion abundance for different components indicates that there are differen ces in solution concentrations or ionization efficiencies for the component s.