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Metal ion-peptide system has been an interesting field of research,providing a basis for understanding metal interactions occurring in biochemistry relevant processes[1,2],Many naturally occurring peptides,such as oxytocin and vasopressin,need to be activated by metal ion for their physiological functions,while the intrinsic interaction and conformational change induced by metal ion is still a challenging problem[3-5],To this end,electrospray ionization mass spectrometry(ESI-MS)is proposed as potential candidates for the study of metal-peptide system.Metal-cationized peptides are induced to the MS by electrospray solution containing the peptide and metal salt.However,the presence and abundance of metal-peptide complex is highly dependent upon solution composition,pH and ligands of metal salt.And signal suppression and dilution effects can not be ignored.Therefore,a new analytical strategy based on MS should be put forward.In this abstract,we propose a new analytical method with “naked” metal ions and peptide ions produced by laser ablation and electrospray,to probe gas-phase interaction of metal ion-peptide.Metal target is ablated by high irradiance laser to yield abundant metal ions,the gas-phase interaction of peptide and metal ion occurs outside the MS inlet.Strong metal-peptide ion can be acquired when laser is on,whereas only protonated peptide ion can be observed with laser off.Combined with collision-induced dissociation(CID),abundant structural information can be provided by metal-peptide ions.Moreover,this method permits us to probe interactions in the absence of solvent effect.Comparison of gas-and solution-phase structures yields important information regarding solvent effect on the molecular structure.Additionally,the relative metal ion affinities of peptides are also discussed.