Development of a High-Throughput Laser-Induced Acoustic Desorption Probe and Raster Sampling For Laser-Induced Acoustic Desorption/Atmospheric Pressure Chemical Ionization

Abstract

Laser-induced acoustic desorption (LIAD) was recently coupled to atmospheric pressure chemical ionization (APCI) and shown to be of great utility for the analysis of a variety of thermally labile nonpolar analytes that are not amenable to ionization via electrospray ionization, such as nonvolatile hydrocarbons. Despite these advancements, LIAD still suffered from several limitations, including only being able to sample a small fraction of the analyte molecules deposited on a Ti foil for desorption, poor reproducibility, as well as limited laser power throughput to the backside of the foil. These limitations severely hinder the analysis of especially challenging analytes, such as asphaltenes. To address these issues, a novel high-throughput LIAD probe and an assembly for raster sampling of a LIAD foil were designed, constructed, and tested. The new probe design allows 98% of the initial laser power to be realized at the backside of the foil over the 25% achieved previously, thus improving reproducibility and allowing for the analysis of large nonvolatile analytes, including asphaltenes. The raster assembly provided a 5.7 fold increase in the surface area of a LIAD foil that could be sampled and improved reproducibility and sensitivity for LIAD experiments. The raster assembly can also improve throughput as foils containing multiple analytes can be prepared and analyzed.

Ion sources for mass spectrometric identification and imaging of molecular species

“…106 Postionization is required in LIAD and has been demonstrated using both SPI 106 and chemical ionization. 107,108 6 Secondary Ion Mass Spectrometry (SIMS) SIMS is perhaps the original MS imaging method: a sample surface is bombarded with a focused beam of high energy primary ions which causes sputtering of the sample surface resulting in the ejection of positive and negative "secondary" ions. 11,109 The desorption/ionization event in SIMS is a highly energetic process that oen leads to extensive fragmentation.…”

Substrate-Mediated Laser Ablation under Ambient Conditions for Spatially-Resolved Tissue Proteomics

“…Ablation processes involving substrate effects were previously described in the literature. However, these mechanisms are different from the SMLA mechanism presented here since in the former case the substrate generally absorbs part of the light, which results in heating 24 , explosive boiling 25 26 27 or in the formation of pressure waves 28 29 30 31 , or then refers to confinement effects such as for nanostructures or nanomaterials 54 55 . However, these processes were shown not to occur here.…”

“…Consequently, heating processes such as those found in Laser-Induced Thermal Desorption (LITD) 24 , explosive boiling 25 26 27 or the emergence of pressure waves (e.g. Laser-Induced Acoustic Desorption (LIAD) 28 29 30 31 ) are not expected to take part in the observed ablation mechanism. On the other hand, the importance of reflection in the observed substrate-mediated effect seems rather to favor a multiphotonic mechanism by simultaneous interaction between the molecules in contact with the substrate and the incident and reflective laser beams during the ns laser irradiation.…”

Laser Desorption/Ablation Postionization Mass Spectrometry: Recent Progress in Bioanalytical Applications

“…LIAD‐APCI, which irradiates the backside of a sample‐attached Ti foil with 532 nm laser pulses and ionizes the desorbed neutrals with a commercial APCI source using CS 2 reagent, has enabled the analysis of a five‐component mixture of hydrocarbons, 5α‐cholestane, and androsterone as well as a petroleum cut with LODs of hydrocarbons in the low ng level (Gao et al, 2011). Reports using different implementations of LIAD‐APCI continue to appear, but are mainly focused on the analysis of petroleum products and explosives (Nyadong et al, 2011; Nyadong et al, 2012; Borton et al, 2013; Ehlert, Walte, & Zimmermann, 2013).…”