New Paradigm in Ionization: Multiply Charged Ion Formation from a Solid Matrix without a Laser or Voltage

Abstract

Laserspray ionization (LSI) is a new approach to producing multiply charged ions from solids on surfaces by laser ablation of matrixes commonly used in matrix-assisted laser desorption/ionization (MALDI). We show that the only necessity of the laser for producing multiply charged ions is to deliver particles or droplets of the matrix/analyte mixture to an ionization zone which is simply a heated inlet to the vacuum of the mass spectrometer. Several other methods for delivering sample are demonstrated to produce nearly equivalent results. One example shows the use of an air gun replacing the laser and producing mass spectra of proteins by shooting pellets into a metal plate which has matrix/analyte applied to the opposite side and near the ion entrance inlet to the mass spectrometer. Multiply charged ions of proteins are produced in the absence of any electric field or laser and with only the need of a heated ion entrance capillary or skimmer. The commonality of the matrix with MALDI and the mild conditions necessary for formation of ions brings into question the mechanism of formation of multiply charged ions and the importance of matrix structure in this process.