The role of the laser pulse duration in infrared matrix-assisted laser desorption/ionization mass spectrometry

Abstract

The role of the laser pulse duration in matrix-assisted laser desorption/ionization mass spectrometry with infrared lasers (IR-MALDI-MS) emitting in the 3 m wavelength range has been evaluated. Mass spectrometric performance and characteristics of the IR-MALDI process were examined by comparing a wavelength-tuneable mid-infrared optical parametric oscillator (OPO) laser of 6 ns pulse duration, tuned to wavelengths of 2.79 and 2.94 m, with an Er:YAG laser ( ϭ 2.94 m) with two pulse durations of 100 and 185 ns, and an Er:YSGG laser ( ϭ 2.79 m) with a pulse duration of 75 ns. Threshold fluences for the desorption of cytochrome C ions were determined as a function of the laser pulse duration for various common IR-MALDI matrices. For the majority of these matrices a reduction in threshold fluence by a factor of 1.2-1.9 was found by going from the 75-100 ns long pulses of the Erbium lasers to the short 6 ns OPO pulse. Within the experimental accuracy threshold fluences were equal for the 100 and the 185 ns pulse duration of the Er:YAG laser. Some pronounced pulse duration effects related to the ion formation from a glycerol matrix were also observed. The effect of the laser pulse length on the duration of ion emission was furthermore investigated. (J Am Soc Mass Spectrom 2002, 13, 975-984)

Computer Simulations of Laser Ablation of Molecular Substrates

“…There is, however, a growing number of experimental studies that are specifically aimed at investigating the fundamental processes in laser ablation. In particular, systematic studies of the role of the laser pulse duration, [11][12][13][14] fluence and wavelength, [15][16][17] size of the laser spot, 15 number of successive laser pulses, 18 laser beam incidence angle, 19,20 initial temperature of the molecular substrate, 21 and molecular volatility 22 have been performed. In addition to the yields 11,15,16,21 and velocities 17,[23][24][25][26][27] of the ejected molecules and ions, that are commonly measured in time-of-flight mass spectrometry experiments, other parameters, such as cluster ejection [28][29][30] and profiles of the acoustic signals propagating from the ablation region [31][32][33][34][35][36][37][38][39] have been investigated, providing a more complete picture of the ablation process.…”

Fragmentation of leucine enkephalin as a function of laser fluence in a MALDI TOF-TOF

“…Several groupsmost notably those of Karas, Hillenkamp, and, more recently, Driesewerd-have studied cluster ejection from the matrix, effects of sample morphology, plume dynamics, and initial velocities [25][26][27][28]. Internal energy coupled into the ions produced by these processes has been investigated by Zenobi and coworkers [29] and by Karas' group [25,30].…”

Target Plate Material Influence on Fullerene-C60 Laser Desorption/Ionization Efficiency

“…Shorter pulses of equal intensity should allow for less heat dissipation time, causing an increased localized heating. Depending on the laser used, the pulse duration can vary from the nanosecondrange, typically used for UV-MALDI (0.3-20 ns) [21,56,57], to picoseconds or even a few femtoseconds. A report comparing nanosecond and femtosecond laser data for fullerene-C 60 found the formed anionic species to be similar, which was ascribed to thermalization in the ablation plasma [58].…”