1 TO DOWNLOAD A COPY OF THIS POSTER NOTE, VISIT WWW.WATERS.COM/POSTERS Mark Towers 1 , Besnik Bajrami 1 , Emrys Jones 1 , Anna Mroz 2 , Zoltan Takats 2 , Emmanuelle Claude 1 , Jim Langridge 1 1 Waters Corporation, Wilmslow, United Kingdom 2 Imperial College London, London, United Kingdom AN INVESTIGATION INTO MULTI-MODEL TISSUE IMAGING ON A SINGLE SECTION BY DESI AND MALDI TOF MASS SPECTROMETRY IMAGING INTRODUCTION Desorption electrospray ionisation (DESI) is an established technique in the field of mass spectrometry, and has been used for tissue imaging (MSI). DESI results are of very high quality for lipids and small molecules, comparable to the more established matrix assisted laser desorption ionisation (MALDI) imaging technique. An additional advantage of DESI is that it can be performed without further sample preparation, such as matrix deposition. Using optimized gas and solvent flow rates, the DESI technique does not damage the tissue surface. Here we present work showing the potential to analyse a single tissue section by DESI imaging with subsequent analysis by MALDI imaging of the same tissue section. In addition we compare to solvent systems for use in DESI and there subsequent effect on the result of imaging by MALDI. METHODS All data was acquired using a SYNAPT G2-Si ion mobility enabled high resolution mass spectrometer (figure 1). The same instrument was used for both the DESI and MALDI analysis by simply exchanging the imaging source. Prior to performing DESI imaging analysis tissue sections were stored at -80°C, and defrosted just before analysis. The slides contained multiple consecutive sections, one section on each was imaged by DESI using either 90% MeOH, 10% water (Solvent A) or 49.5% MeOH, 49.5% chloroform, 1% water (Solvent B). After DESI analysis the tissue sections were stored at 4°C, whilst the instrument was converted to MALDI configuration. For MALDI analysis the tissue sections were spray coated with 9-Aminoacridine (5mg/ ml in 80% EtOH, 10% water, 30 layers, 20 μl/min) using a Suncollect™ sprayer. In each case the tis-sue section analyzed by DESI was re-analyzed by MALDI, from the same slide a pristine (non DESI imaged) section was also acquired for comparison. Tissue sections The tissue sections analyzed were consecutive sections from a human colorectal adenocarcinoma. The tissue sample was snap frozen in liquid nitrogen and stored at - 80°C, prior to cryosectioning at a 10 μm thickness. The tissue samples consisted mainly of two tissue types: tumor and connective tissue. Samples from this tissue set have previously been analyzed and results published by Oetjen et al (2015).[1]