Laser-Induced Acoustic Desorption Mass Spectrometry

Abstract

Large thermally labile molecules were not amenable to mass spectrometric analysis until the development of atmospheric pressure evaporation/ionization methods, such as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI), since attempts to evaporate these molecules by heating induces degradation of the sample. While ESI and MALDI are relatively soft desorption/ionization techniques, they are both limited to preferential ionization of acidic and basic analytes. This limitation has been the driving force for the development of other soft desorption/ionization techniques. One such method employs laser-induced acoustic desorption (LIAD) to evaporate neutral sample molecules into mass spectrometers. LIAD utilizes acoustic waves generated by a laser pulse in a thin metal foil. The acoustic waves travel through the foil and cause desorption of neutral molecules that have been deposited on the opposite side of the foil. One of the advantages of LIAD is that it desorbs low-energy molecules that can be ionized by a variety of methods, thus allowing the analysis of large molecules that are not amenable to ESI and MALDI. This review covers the generation of acoustic waves in foils via a laser pulse, the parameters affecting the generation of acoustic waves, possible mechanisms for desorption of neutral molecules, as well as the various uses of LIAD by mass spectrometrists. The conditions used to generate acoustic or stress waves in solid materials consist of three regimes: thermal, ablative, and constrained. Each regime is discussed, in addition to the mechanisms that lead to the ablation of the metal from the foil and generation of acoustic waves for two of the regimes. Previously proposed desorption mechanisms for LIAD are presented along with the flaws associated with some of them. Various experimental parameters, such as the exact characteristics of the laser pulse and foil used, are discussed. The internal and kinetic energy of the neutral desorbed molecules are also considered. Our research group has been instrumental in the development and use of LIAD. For example, we have systematically examined the influence of many parameters, such as the type of the foil and its thickness, as well as the analyte layer's thickness, on the efficiency of desorption of neutral molecules. The coupling of LIAD with different instruments and ionization techniques allows for broad use of LIAD in our research laboratories. The most important applications involve analytes that cannot be analyzed by using other mass spectrometric methods, such as large saturated hydrocarbons and heavy hydrocarbon fractions of petroleum. We also use LIAD to characterize lipids, peptides, and oligonucleotides. Fundamental research on the reactions of charged mono-, bi-, and polyradicals with biopolymers, especially oligonucleotides, also requires the use of LIAD, as well as thermochemical measurements for neutral biopolymers. These are but a few of the uses of LIAD in our research group.

On‐Surface Synthesis of Atomically Precise Graphene Nanoribbons

“…[ 13,15,[17][18][19] The size of the precursor molecule is ultimately limited by the requirement that the entire molecule must evaporate upon heating, not decompose in the crucible. Alternatives to molecular beam epitaxy (MBE), such as electrospray deposition [ 20 ] or laser-induced desorption, [ 21 ] offer ways to overcome this limitation, as does the concept of hierarchical growth. [ 22 ] These routes are yet to be explored in the context of the on-surface synthesis of GNRs.…”

Properties and Reactivity of Gaseous Distonic Radical Ions with Aryl Radical Sites

“…286,287 LIAD was reviewed in 2012. 288 LIAD enabled the expansion of the study of the reactivity of aryl mono- and diradicals to peptides and oligonucleotides, which facilitated the acquisition of more relevant information about protein and DNA degradation by aryl radicals. In 2009, two charged phenyl radicals, the N -phenyl-3-dehydropyridinium cation (the N -phenyl derivative of 17 ; Chart 3) and the N -(3-dehydrophenyl) pyridinium cation ( 14 , Chart 2), were allowed to react with several dipeptides desorbed by LIAD into an FT-ICR mass spectrometer.…”

Laser pulse duration dependence of blister formation on back-radiated Ti thin films for BB-LIFT

“…Multiple techniques have been developed to enable the gentle transfer, such as matrix-assisted laser desorption/ ionisation (MALDI), electrospray, and laser-induced acoustic desorption (LIAD) [5] being some of the most common. MALDI utilises the direct vaporisation of a matrix that contains the particles of interest.…”