title: Development and characterization of an ionization technique for analysis of biological macromolecules: liquid matrix-assisted laser desorption electrospray ionization.
abstract: We have developed an atmospheric pressure ionization technique called liquid matrix-assisted laser desorption electrospray ionization (liq-MALDESI) for the generation of multiply charged ions by laser desorption from liquid samples deposited onto a stainless steel sample target biased at a high potential. This variant of our previously reported MALDESI source does not utilize an ESI emitter to postionize neutrals. Conversely, we report desorption and ionization from a macroscopic charged droplet. We demonstrate high mass resolving power single-acquisition FT-ICR-MS analysis of peptides and proteins ranging from 1 to 8.6 kDa at atmospheric pressure. The liquid sample acts as a macroscopic charged droplet similar to those generated by electrospray ionization, whereby laser irradiation desorbs analyte from organic matrix containing charged droplets generating multiply charged ions. We have observed a singly charged radical cation of an electrochemically active species indicating oxidation occurs for analytes and therefore water; the latter would play a key role in the mechanism of ionization. Moreover, we demonstrate an increase in ion abundance and a concurrent decrease in surface tension with an increase in the applied potential.
authors.affiliation: W.M. Keck FT-ICR Mass Spectrometry Laboratory, Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, USA.
authors.forename: Jason S
authors.initials: JS
authors.lastname: Sampson
authors.forename: Adam M
authors.initials: AM
authors.lastname: Hawkridge
authors.forename: David C
authors.initials: DC
authors.lastname: Muddiman
mesh_terms: D009930:Organic Chemicals / Q000737:chemistry; D010455:Peptides / Q000032:analysis*; D011506:Proteins / Q000032:analysis*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013499:Surface Properties
chemical_list: D009930:Organic Chemicals; D010455:Peptides; D011506:Proteins