General Guidelines for Sample Preparation Strategies in HR-$\mu$MAS NMR-based Metabolomics of Microscopic Specimens

International audience; The study of the metabolome within tissues, organisms, cells or biofluids can be carried out by several bioanalytical techniques. Among them, nuclear magnetic resonance (NMR) is one of the principal spectroscopic methods. This is due to a sample rotation technique, high-resolution magic angle spinning (HR-MAS), which targets the analysis of heterogeneous specimens with a bulk sample mass from 5 to 10 mg. Recently, a new approach, high-resolution micro-magic angle spinning (HR-$\mu$MAS), has been introduced. It opens, for the first time, the possibility of investigating microscopic specimens (