Integrated multichannel microchip electrospray ionization mass spectrometry: analysis of peptides from on-chip tryptic digestion of melittin.

In continuation of our work to develop an integrated multichannel microchip interfaced to electrospray mass spectrometry (ESI-MS), this paper demonstrates one of several applications of this approach in monitoring tryptic digestion products. The multichannel microchip allowed integration of sample preparation onto the microchip to facilitate the analysis process. Melittin was selected as a model oligopeptide because it possesses a cluster of four adjacent basic residues which enable probing the site specificity of trypsin as a function of digest times. Reactions were performed on-chip in different wells for specific time periods and then analyzed by infusion from the microchip by ESI-MS, using leucine enkephalin as internal standard. The rate of formation and disappearance of the molecular ion and individual fragments was followed for a melittin to trypsin concentration ratio of 300:1. The results indicate the potential of integrating enzymatic reactions with multichannel microchip ESI-MS for automated optimization of reaction condition while consuming only small amounts of sample.