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Laser Beam Filtration for High Spatial Resolution MALDI Imaging Mass Spectrometry

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Journal of The American Society for Mass Spectrometry

Abstract

We describe an easy and inexpensive way to provide a highly defined Gaussian shaped laser spot on target of 5 μm diameter for imaging mass spectrometry using a commercial MALDI TOF instrument that is designed to produce a 20 μm diameter laser beam on target at its lowest setting. A 25 μm pinhole filter on a swivel arm was installed in the laser beam optics outside the vacuum ion source chamber so it is easily flipped into or out of the beam as desired by the operator. The resulting ion images at 5 μm spatial resolution are sharp since the satellite secondary laser beam maxima have been removed by the filter. Ion images are shown to demonstrate the performance and are compared with the method of oversampling to achieve higher spatial resolution when only a larger laser beam spot on target is available.

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Acknowledgement

The authors acknowledge support for this project by grants from the National Institute of General Medical Sciences 8 P41 GM103391-02 (formerly NCRR 5P41RR031461-02) and 5R01GM058008-13, and the Department of Defense W81XWH-05-1-0179.

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Authors and Affiliations

  1. Departments of Biochemistry, Mass Spectrometry Research Center, National Research Resource for Imaging Mass Spectrometry, Vanderbilt University, Nashville, TN, USA

    Andre Zavalin, Junhai Yang & Richard Caprioli

  2. Department of Pharmacology, Medicine, and Chemistry, Vanderbilt University, Nashville, TN, USA

    Richard Caprioli

Authors
  1. Andre Zavalin
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  2. Junhai Yang
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  3. Richard Caprioli
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Corresponding author

Correspondence to Richard Caprioli.

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Figure 1S

(A) and (B) MS negative ion mode lipid images of mouse cerebellum at a 5 μm raster using following laser beam parameters: (A) unfiltered oversampling laser beam; (B), a 5 μm diameter spatially filtered laser beam without oversampling. The MS images in (A) and (B) are an RGB mix of 3 MS images: m/z 766.5 (green), m/z 716.5 (blue), and m/z 888 (red). The composite MS image is overlaid on an optical microscope DIC image. (C) is an H&E stained optical image of the sample B after MS image acquisition. (D), (E) are zoomed MS ion images at m/z 888 in greyscale. (D) unfiltered oversampled laser beam, (E) 5 μm spatially filtered laser beam without oversampling, (F) non-normalized negative ion mode lipid mass spectra (top spectrum in (F) acquired with spatially filtered laser beam, and the bottom spectrum acquired by oversampling the laser beam without the pinhole filter. (JPEG 137 kb)

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Zavalin, A., Yang, J. & Caprioli, R. Laser Beam Filtration for High Spatial Resolution MALDI Imaging Mass Spectrometry. J. Am. Soc. Mass Spectrom. 24, 1153–1156 (2013). https://doi.org/10.1007/s13361-013-0638-5

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  • DOI: https://doi.org/10.1007/s13361-013-0638-5

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