New surfaces for desorption electrospray ionization mass spectrometry: porous silicon and ultra‐thin layer chromatography plates

Abstract

The performance of nanoporous silicon (pSi) and ultra-thin layer chromatography (UTLC) plates as surfaces for desorption electrospray ionization (DESI) was compared with that of polymethyl methacrylate (PMMA) and polytetrafluoroethylene (PTFE), both popular surfaces in previous DESI studies. The limits of detection (LODs) and other analytical characteristics for six different test compounds were determined using all four surfaces. The LODs for the compounds were in the fmol-pmol (pg-ng) range. The LODs with the pSi surface were further improved for each of the compounds when heat was applied to the surface during sample application which gave LODs as low as or lower than those achieved with PMMA and PTFE. The UTLC plates were successfully used as a rapid means of chromatographic separation prior to DESI-MS analysis. Another advantage achieved using the newer pSi and UTLC surfaces was increased speed of analysis, associated with drying of solution-phase samples. This took place immediately at the UTLC surface and it could be achieved rapidly by gently heating the pSi surface. The presence of salts in the sample did not cause suppression of the analyte signal with any of the surfaces.

The influence of material and mesh characteristics on transmission mode desorption electrospray ionization

“…Surface variables including the chemical composition, porosity, texture, and electrical conductivity of the substrate have been reported to affect DESI analyses [2,24,[37][38][39]. Dramatic reductions in response have been noted for high conductivity surfaces due to neutralization of the incoming ion plume at the surface [2,38].…”

“…If a more volatile solvent is used (e.g., methanol), the evaporation time may be reduced; however the low surface tension of the solvent makes uniform sample deposition more challenging [2]. Furthermore, sample analyses that utilize smooth surfaces are typically prone to erosion effects, thereby requiring alternative deposition onto porous or rough surfaces that retain the adsorbed analyte during the formation of the initial solvation layer [2,37,39]. The mesh materials used for TM-DESI overcome these difficulties by suspending both high and low volatility deposition solvents of varying surface tensions in the open space of a mesh.…”

“…Dramatic reductions in response have been noted for high conductivity surfaces due to neutralization of the incoming ion plume at the surface [2,38]. Variations in response due to the impact of the surface on crystallization of deposited samples have been reported [2,37], as well as increases in response for porous or rough surfaces due to a reduction in sample spreading [2,37], and increases in response due to chemical inertness and hydrophobicity of materials such as PTFE [24,38]. DESI analyses have utilized a variety of surface materials, including glass, PMMA, PTFE, TLC plates, UTLC plates, porous silicon, nanoporous aluminum, paper, and stainless steel.…”

“…In this adaptation, the incident spray angle and collection angle are fixed at 0°and the spray is transmitted through the sample (Figure 1). Along with the simplification of the experimental geometry, the transmission mode also allows convenient analysis of both dry (i.e., following evaporation of the deposition solvent) and wet (i.e., solvated) samples with similar performance characteristics to those achieved using traditional DESI [36].Surface variables including the chemical composition, porosity, texture, and electrical conductivity of the substrate have been reported to affect DESI analyses [2,24,[37][38][39]. Dramatic reductions in response have been noted for high conductivity surfaces due to neutralization of the incoming ion plume at the surface [2,38].…”

Three‐Dimensional Vizualization of Mouse Brain by Lipid Analysis Using Ambient Ionization Mass Spectrometry

“…Indeed, it has been shown that several experimental parameters can be optimized to improve the quality of DESI data. [9,15] Two distinctive mass spectral patterns were observed in the negative-ion mode for the brain sections analyzed depending on the region of the brain being investigated (Figure 1). The differences are associated with the lipid compositions representative of the gray and white matter of the brain.…”