Static secondary ion mass spectrometry to monitor solid-phase peptide synthesis.

Insights into the direct monitoring of supported peptide synthesis were realized through the design of time of flight static secondary ion mass spectrometry (TOF-S-SIMS) experiments. The mass spectrometric method was carried out at the resin bead level and was found reproducible (intra- and inter-day assays), sensitive (femtomol level) and non-destructive (only 0.01% of the peptides were destroyed by the primary ion beam bombardment). The nature of the peptide-resin linkage governed the recovery of ions characterizing the whole peptide sequence. A S-SIMS cleavable bond was thus required solely in that position to achieve the release of the growing structures from the insoluble support into the gas phase without any fragmentation. Results are presented with standard solid-phase resins allowing linkage through an amide or an ester bond. The latter was orthogonally broken upon the bombardment and thus constituted a convenient S-SIMS cleavable bond.