High-Reactivity Matrices Increase the Sensitivity of Matrix Enhanced Secondary Ion Mass Spectrometry

Abstract

Secondary ion mass spectrometry (SIMS) is a desorption/ionization method in which ions are generated by the impact of a primary ion beam on a sample. Classic matrix assisted laser desorption and ionization (MALDI) matrices can be used to increase secondary ion yields and decrease fragmentation in a SIMS experiment, which is referred to as matrix enhanced SIMS (ME-SIMS). Contrary to MALDI, the choice of matrices for ME-SIMS is not constrained by their photon absorption characteristics. This implies that matrix compounds that exhibit an insufficient photon absorption coefficient have the potential of working well with ME-SIMS. Here, we evaluate a set of novel derivatives of the classical MALDI matrices α-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB) for usability in ME-SIMS. This evaluation was carried out using peptide mixtures of different complexity and demonstrates significant improvements in signal intensity for several compounds with insufficient UV absorption at the standard MALDI laser wavelengths. Our study confirms that the gas-phase proton affinity of a matrix compound is a key physicochemical characteristic that determines its performance in a ME-SIMS experiment. As a result, these novel matrices improve the performance of matrix enhanced secondary ion mass spectrometry experiments on complex peptide mixtures.

Effects of a proton‐conducting ionic liquid on secondary ion formation in time‐of‐flight secondary ion mass spectrometry

“…However, not all values of GBs and PAs of ionic‐liquid components are known; hence, it seems impossible to select ionic liquids just on the basis of literature data on GBs and PAs. In addition, although GBs and PAs are important factors in proton‐transfer reactions, other factors can also affect molecular secondary ion yields . For these reasons, selecting ionic liquids suitable for primary ion beams is one of the most important issues to be investigated in the future.…”

“…In SIMS, it seems that ionization is promoted via the transfer of protons from (or to) a PIL matrix . Unlike MALDI, however, the choice of SIMS matrices will not have to be constrained by their photon absorption characteristics …”

“…[41] Unlike MALDI, however, the choice of SIMS matrices will not have to be constrained by their photon absorption characteristics. [8,44] Recently, we have performed SIMS experiments using a PIL, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), [45] which has high protonic conductivity even at room temperature. [46,47] Then, we reported that [dema][TfO] acted effectively as a primary ion beam as well as a liquid matrix to increase protonated secondary ions of arginine.…”

Sample preparation for mass spectrometry imaging: Small mistakes can lead to big consequences

“…For ME-SIMS the possible selection of a matrix is widened beyond the traditional MALDI matrix compounds that require a specific photon absorption profile. Examination of novel derivatives of the standard CHCA and DHB has been tested for applicability to ME-SIMS [115]. Surface metallization by plasma coating has also been reported to aid membrane biomolecules (lipids and sterols) imaging by SIMS.…”

Comparing C60+ and (H2O)n+ clusters for mouse brain tissue analysis

“…[3] There have been efforts to enhance secondary ion yields by adding metallic nanoparticles or matrix-assisted laser desorption/ionization type matrices to the sample. [5,12] Successful attempts to increase secondary ion yields involved the enhancement of the protonation of ions with the presence of water during the analysis. [6][7][8] There have been attempts to analyse the sample in a frozen hydrated state (instead of freeze-drying the sample) [9][10][11]13] or to inject water vapour at the sample's surface.…”