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

Abstract

A simple device is described for desolvation of highly charged matrix/analyte clusters produced by laser ablation leading to multiply charged ions that are analyzed by ion mobility spectrometry-mass spectrometry. Thus, for example, highly charged ions of ubiquitin and lysozyme are cleanly separated in the gas phase according to size and mass (shape and molecular weight) as well as charge using Tri-Wave ion mobility technology coupled to mass spectrometry. This contribution confirms the mechanistic argument that desolvation is necessary to produce multiply charged matrix-assisted laser desorption/ionization (MALDI) ions and points to how these ions can be routinely formed on any atmospheric pressure mass spectrometer. (J Am Soc Mass Spectrom 2010, 21, 1260 -1264 -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]. Full range mass spectra of bovine insulin were obtained on as little as 40 fmol when applying ion transfer capillary temperatures of ϳ350°C [3].The unique feature of LSI to produce highly charged ions using direct laser ablation of a solid surface enhances fragmentation as was demonstrated by obtaining nearly complete protein sequence coverage of ubiquitin using electron-transfer dissociation (ETD) technology on a LTQ mass spectrometer [3]. Initial laserspray applications demonstrated the ability to produce singly charged lipid ions from mouse brain tissue under ambient conditions [1]. Using transmission geometry the matrix treated tissue sections were passed free-hand through the focused laser beam in front of the mass spectrometer orifice (Orbitrap Exactive) obtaining a spatial resolution of Ͻ100 m [1]. The objective is to observe proteins from tissue.Ion mobility spectrometry (IMS) MS has many advantages compared with even high-resolution mass spectrometers because of its ability to extend the dynamic range and separate isomeric composition [4][5][6][7]. This is possible because ions are separated in the IMS dimension according to charge and cross-section (size and shape) [8][9][10][11]. One key benefit of this solvent-free gas-phase separation by IMS is that when combined with solvent-free sample preparation [12] achieves total solvent-free analysis by MS entirely decoupling ionization, separation, and mass analyses fro...

Localization and imaging of gangliosides in mouse brain tissue sections by laserspray ionization inlet

“…Approximately 20 laser shots were summed for each spectrum. LSII-MS was performed on the SYNAPT G2 by converting the nano-ESI source to a LSII source according to published procedure (54)(55)(56)(57)(58)(59)68 ) using the 337 nm nitrogen laser employed for LSII-MS on the LTQ Velos.…”

“…Singly deprotonated ions mass spectrometer is an important LSII parameter in both positive and negative ion mode detection ( 65 ). Ion abundance in LSII is increased by heating the ion transfer capillary ( 53,(68)(69)(70). Using 2,5-DHB on a LTQ Velos mass spectrometer, GD1 could only be analyzed at capillary temperatures between 400°C and the maximum setting of 450°C in the negative ion mode.…”

Laserspray ionization using an atmospheric solids analysis probe for sample introduction

“…The Waters Corporation (Milford, MA, USA) SYNAPT G2 nanospray source was modified as previously described [4]. Briefly, the laser beam from a Spectra Physics nitrogen 337-VSL-ND-S laser was aimed through the opening created by removal of the LockSpray mechanism and directly in-line with the skimmer entrance.…”

“…The nanospray capillary was also removed so that a melting point tube could be attached to the x,y,z-stage normally used to adjust the capillary relative to the ion entrance orifice for ESI. A desolvation device described elsewhere [4] was heated to ca. 250°C.…”

“…(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]. Transmission geometry was used to obtain data for the original LSI publications in the absence of any applied voltage [1][2][3].…”