Electrospray-assisted laser desorption/ionization and tandem mass spectrometry of peptides and proteins

We have constructed an electrospray‐assisted laser desorption/ionization (ELDI) source which utilizes a nitrogen laser pulse to desorb intact molecules from matrix‐containing sample solution droplets, followed by electrospray ionization (ESI) post‐ionization. The ELDI source is coupled to a quadrupole ion trap mass spectrometer and allows sampling under ambient conditions. Preliminary data showed that ELDI produces ESI‐like multiply charged peptides and proteins up to 29 kDa carbonic anhydrase and 66 kDa bovine albumin from single‐protein solutions, as well as from complex digest mixtures. The generated multiply charged polypeptides enable efficient tandem mass spectrometric (MS/MS)‐based peptide sequencing. ELDI‐MS/MS of protein digests and small intact proteins was performed both by collisionally activated dissociation (CAD) and by nozzle‐skimmer dissociation (NSD). ELDI‐MS/MS may be a useful tool for protein sequencing analysis and top‐down proteomics study, and may complement matrix‐assisted laser desorption/ionization (MALDI)‐based measurements. Copyright © 2007 John Wiley & Sons, Ltd.