Laser desorption substrate effects

Surface mass spectrometry of molecular species

“…The two substrate-wavelength combinations lead to different extents of fragmentation, owing to different desorption mechanisms and/or different energy transfer efficiencies from the substrate to desorbed species. 52 These experiments utilized the same laser postionization scheme (see below). Fragmentation during laser desorption and post-ionization is discussed further below.…”

“…Slow thermal desorption (TDS) imparts the least, laser-induced thermal desorption imparts an intermediate amount and sputtering imparts the most internal energy to a desorbed neutral. 28,52,104 The coupling of the molecule to the surface and/or the substrate itself will also have an effect upon the internal energy of the desorbed molecule. The effect of substrate and/or desorption method is demonstrated by L2MS of the tripeptide glutathione, which undergoes more extensive fragmentation during 1064 nm laser desorption from Ta [ Fig.…”

“…The desorption/ionization method can be tuned to suppress or enhance fragmentation. 52 Coincidence counting can correlate specific fragment ions to their metastable parent ions. 80 The analyte ion can be mass isolated in the gas phase, then induced to undergo collision-induced dissociation with a background gas.…”

Matrix‐free methods for laser desorption/ionization mass spectrometry

“…One approach for the analysis of small molecules is the direct desorption/ ionization of analytes. For instance, one study directly deposited tryptophan on a sample plate and then irradiated it with a laser to desorb and ionize the analyte (Zhan, Wright, & Zenobi, 1997). The method was limited to analytes with a m/z below 2,000, and is very dependent on the properties of the analyte.…”

Recent Developments in the Chemistry and Chemical Applications of Porous Silicon

“…Energy accumulated from the laser pulse by the matrix is transferred to the incorporated analyte; this exchange induces vaporization and ionization of the dispersed molecules which are then detected and measured by time-of-flight (TOF) mass spectrometry. In contrast to direct desorption/ionization methods from matrix-less surfaces that may yield a plethora of fragmented ion products from a single analyte, MALDI-MS is considered a ''soft'' ablation technique in that the energy transfer is indirect and relatively gentle, substantially reducing the extent of ion degradation and simplifying the interpretation of the mass spectra [121][122][123][124][125][126]. Furthermore, its sensitivity to femtomolar and attomolar levels of analytes and its tolerance for mixtures and biological contaminants afford the characterization of minimal sample sizes of only modest purity.…”