Technical Note Cite This: Anal. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/ac
Oversampling To Improve Spatial Resolution for Liquid Extraction Mass Spectrometry Imaging Kyle D. Duncan and Ingela Lanekoff* Department of Chemistry-BMC, Uppsala University, Uppsala, Sweden S Supporting Information *
ABSTRACT: Liquid extraction mass spectrometry imaging (MSI) experiments provide users with direct analysis of biological surfaces with minimal sample preparation. Until now, much of the effort to increase spatial resolution for MSI with liquid extraction techniques has focused on reducing the size of the sampling area. However, this can be experimentally challenging. Here, we present oversampling as a simple alternative to increase the spatial resolution using nanospray desorption electrospray ionization (nano-DESI) MSI. By imaging partial rat spinal cord tissue sections, two major concerns with oversampling are addressed: whether endogenous molecules are significantly depleted from repeated sampling events and whether analytes are redistributed as a result of oversampling. In depth examination of ion images for representative analytes show that depletion and redistribution do not affect analyte localization in the tissue sample. NanoDESI MSI experiments using three times oversampling provided higher spatial resolution, allowing the observation of features not visible with undersampling. Although proper care must be taken to ensure that oversampling will work in specific applications, we envision oversampling as a simple approach to increase image quality for liquid extraction MSI techniques.
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the stepping size between each line scan across the sample surface. As recently developed mass spectrometers continue to provide faster duty cycles, the biggest challenge to improve spatial resolution for liquid extraction MSI techniques is focused on reducing the stepping size between each line scan across the sample surface. In DESI, this has been achieved by reducing the size of the emitter tip8,9 and by carefully optimizing the experimental parameters, such as spray tip-tosurface distance and solvent flow rate.10,11 In nano-DESI, the spatial resolution has been increased by reducing the size of the continuously flowing liquid bridge in contact with the sample surface by reducing the outer diameter of the capillaries.12−14 To date, the lowest reported stepping size between line scans is
