| Abstract
| - We show that highly charged ions can be generated if apulsed infrared laser and a glycerol matrix are employedfor atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry with a quadrupole iontrap. Already for small peptides like bradykinin, doublyprotonated ions form the most abundant analyte signalin the mass spectra. The center of the charge-statedistribution increases with the size of the analyte. Forexample, insulin is detected with a most abundant ionsignal corresponding to a charge state of four, whereasfor cytochrome c, the 10 times protonated ion speciesproduces the most intense signal. Myoglobin is observedwith up to 13 charges. The high m/z ratios allow us touse the Paul trap for the detection of MALDI-generatedprotein ions that are, owing to their high molecular weight,not amenable in their singly protonated charge state.Formation of multiple charges critically depends on theaddition of diluted acid to the analyte−matrix solution.Tandem mass spectra generated by collision-induceddissociation of doubly charged peptides are also presented. The findings allow speculations about the involvement of electrospray ionization processes in these MALDIexperiments.
|
