1. National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory, Teddington, Middlesex TW11 0LW, U.K.
2. Surface Technology Group, National Physical Laboratory, Teddington, Middlesex TW11 0LW, U.K.
3. Physikalisches Institut, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, Münster 48149, Germany
4. Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, London SW7 2AZ, U.K.
5. ,The Rosalind Franklin Institute, Harwell Campus, Didcot OX11 0FA, U.K.