ToF-SIMS Investigation\nof Environmental Effects on\nAnalyte Migration in Matrix Coatings for Mass Spectrometry Imaging\nUsing a Newly Developed Vapor Deposition System

High resolution mass spectrometry images are of increasing\nimportance\nin biological applications, such as the study of tissues and single\ncells. Two promising techniques for this are matrix-enhanced secondary\nion mass spectrometry (ME-SIMS) and matrix-assisted laser desorption/ionization\n(MALDI). For both techniques, the sample of interest must be coated\nwith a matrix prior to analysis, and analytes must migrate into the\nmatrix. The mechanisms involved in this migration and the factors\nthat influence the migration are poorly understood, which lead to\ndifficulties with reproducibility. In this work, a sublimation matrix\ncoater with an effusion cell and sample cooling was developed and\nbuilt in-house for controlled physical vapor deposition. In this system,\nsample transfer between the coater and mass spectrometer is possible\nwithout breaking vacuum, which facilitates the study of environmental\ninfluences on analyte migration. The influence of exposure to ambient\nair on the migration of two analytes (a lipid and a peptide), which\nwere coated with the matrix α-cyano-4-hydroxycinnamic acid (CHCA),\nwas studied using 3D-SIMS imaging. Although the distribution of analyte\nin the matrix changed very little after 21 h of storage in vacuum,\nsignificant redistribution of the analyte was observed after exposure\nto ambient air. The magnitude of the effect was greater for the lipid\nthan for the peptide. Further work is needed to determine the role\nof humidity in the redistribution process and the impact of analyte\nredistribution on MALDI measurements.