Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Method for Selectively Producing Either Singly or Multiply Charged Molecular Ions

Abstract

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is noted for its ability to produce primarily singly charged ions. This is an attribute when using direct ionization for complex mixtures such as protein digests or synthetic polymers. However, the ability to produce multiply charged ions, as with electrospray ionization (ESI), has advantages such as extending the mass range on mass spectrometers with limited mass-to-charge (m/z) range and enhancing fragmentation for structural characterization. We designed and fabricated a novel field free transmission geometry atmopsheric pressure (AP) MALDI source mounted to a high-mass resolution Orbitrap Exactive mass spectrometer. We report the ability to produce at will either singly charged ions or highly charged ions using a MALDI process by simply changing the matrix or the matrix preparation conditions. Mass spectra with multiply charged ions very similar to those obtained with ESI of proteins such as cytochrome c and ubiquitin are obtained with low femtomole amounts applied to the MALDI target plate and for peptides such as angiotensin I and II with application of attomole amounts. Single scan acquisitions produce sufficient ion current even from proteins.

Laserspray ionization (LSI) ion mobility spectrometry (IMS) mass spectrometry

“…was recently introduced on a Thermo Fisher Scientific Orbitrap Exactive [1][2][3]. The principle of this ionization method is that the analyte/matrix sample is ablated by the use of a laser operating at atmospheric pressure (AP) and ions are subsequently formed from highly charged matrix/analyte clusters during a desolvation process.…”

“…The free choice of charge state selection demonstrates the utility of LSI for the analysis of complex mixtures. Singly charged ions similar to those obtained with matrix-assisted laser desorption/ ionization (MALDI) or multiply charged ions similar to those produced by electrospray ionization (ESI) [2] can be selected using LSI. Multiply charged ions are especially beneficial for providing the ability to ionize by laser ablation larger molecules such as proteins and synthetic polymers on high-performance but mass range limited mass spectrometers such as the Orbitrap Exactive [2,3].…”

Homogeneous Matrix Deposition on Dried Agar for MALDI Imaging Mass Spectrometry of Microbial Cultures

“…As inferred from Figure 1c, such small laser foci could easily come across matrix-free regions when the standard sieving technique is used. This is different from dry matrix applications on tissue samples, where the dry method allows high resolution imaging [18]. Other matrix application methods such as precoating of the target as shown by Grove et al [19] is supposedly not suitable for agar-based samples owing to the thickness and density of the dried agar compared with a tissue section (i.e., the laser will not penetrate the agar sample).…”

Laserspray ionization using an atmospheric solids analysis probe for sample introduction

“…Mass spectra were obtained at high-resolution and using ion mobility spectrometry/MS. (J Am Soc Mass Spectrom 2010, 21, 1889 -1892) © 2010 Published by Elsevier Inc. on behalf of American Society for Mass Spectrometry T he recently introduced laserspray ionization (LSI) mass spectrometry (MS) technique has advantages similar to ESI MS in mass range extension and improved fragmentation related to multiple charging, as well as the advantages of fast direct analysis and laser ablated spatial resolution associated with matrixassisted laser desorption/ionization (MALDI) [1,2]. The LSI method has been demonstrated on atmospheric pressure ionization (API) instruments from two MS manufacturers [1][2][3][4].…”

“…The LSI method has been demonstrated on atmospheric pressure ionization (API) instruments from two MS manufacturers [1][2][3][4]. Transmission geometry was used to obtain data for the original LSI publications in the absence of any applied voltage [1][2][3]. A nitrogen laser beam strikes the backside of the matrix/analyte deposited on the opposite side of a glass microscope slide relative to the laser and near the ion entrance orifice of the mass spectrometer.…”