Laser desorption in transmission geometry inside a Fourier-transform ion cyclotron resonance mass spectrometer

Abstract

We report here the first application of laser desorption (LD) in transmission geometry (backside irradiation of the sample through a transparent support) inside a Fourier-transform ion cyclotron resonance mass spectrometer (FT-ICR). A probe-mounted fiber optic assembly was used to simplify the implementation of this LD technique. This setup requires little or no instrument modifications, has minimum maintenance requirements, and is relatively inexpensive to build. The performance of the probe was tested by determining the molecular weight of a commercial polystyrene standard from its matrix-assisted laser desorption/ionization (MALDI) spectrum. The measured average molecular weight is comparable to that obtained for the same sample by MALDI in the conventional top-illumination arrangement (reflection geometry) and by the manufacturer of the sample by gel permeation chromatography. The average velocities measured for ions evaporated by transmission mode LD of several neat samples are about half the velocity of those obtained by using the reflection geometry. Therefore, transmission mode irradiation of the sample holds promise to desorb ions that are easier to trap in an ICR cell. An oscillating capillary nebulizer was adapted for the deposition of analytes to improve sampling reproducibility.

Design and Characterization of a High-Power Laser-Induced Acoustic Desorption Probe Coupled with a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer

“…15 The results indicate that higher irradiances aid in the evaporation of molecules of higher molecular weights, likely because larger amplitude acoustic waves are generated. 16 These trends were observed for power densities ranging from 5.4 × 10 8 W/cm 2 to 9.0 × 10 8 W/cm 2 and are attributed to the generation of acoustic waves with larger amplitudes within the Ti foil.…”

“…15 The flight times were examined by measuring the molecular ion signal intensity, obtained with EI, of a LIAD evaporated analyte after different flight times. The sequence of events is outlined in Figure 6.…”

Experimental Investigations of the Internal Energy of Molecules Evaporated via Laser-Induced Acoustic Desorption into a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer

“…Both instruments were configured with a specially made guide ring for positioning of the LIAD probe with respect to the center of the ICR cell, as described previously. 10,14,20,21 Desorption is performed by focusing the laser beam of a Nd:YAG laser (532 nm, 3 ns pulse width) through an optical fiber (365 μm diameter, 3M Specialty Fibers, West Haven, CT) onto the back side of a Ti metal foil secured on the probe tip, as previously described. 10,14 The two transmission geometry probes are of different diameters (1/2″ and 7/8″).…”

Laserspray ionization using an atmospheric solids analysis probe for sample introduction

“…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. Previously, transmission geometry AP-MALDI experiments reported only singly charged ions [5][6][7][8]. It has been shown not to be necessary for the laser beam to pass through the glass to obtain multiply charged ions of peptides [1,9].…”