This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/rcm.8652 This article is protected by copyright. All rights reserved. Desport Jessica (Orcid ID: 0000-0002-1847-7646) MSPolyCalc: a web-based App for polymer mass spectrometry data interpretation. The case study of a pharmaceutical excipient. Jessica S Desport, 1 Gilles Frache, 1 Luc Patiny 2,* 1 LIST - Luxembourg Institute of Science and Technology, Material, Research and Technology department, 41 rue du Brill, L-4422 Belvaux, Luxembourg 2 Zakodium Sàrl, chemin des Plantaz 10, CH-1440, Montagny-Chamard, Switzerland *corresponding author: luc.patiny@zakodium.com Abstract Rationale: In contrast to biological polymers, synthetic macromolecules consist of distributions of size, chemical composition, functionality and eventually architecture. The mass spectrum of a synthetic polymer may exhibit a tremendous amount of signals. The availability of suitable IT tools to support interpretation is key. Methods: A web-based tool is presented: MSPolyCalc. It offers a set of functionalities, including the calculation of polymer distributions molecular formulae and a match evaluation for peak assignment based on both mass and spectral accuracy (similarity score). The software was successfully tested with mass spectra exhibiting resolutions ranging from 10 000 to 240 000. Results: The molecular characterization of a synthetic poly(ethylene glycol)-based excipient was achieved. MSPolyCalc allowed the discrimination of six polymer compositions of variable relative abundance. Secondary ionization adducts with very low intensity consisting of matrix- analyte clusters were also successfully identified. Conclusions: MSPolyCalc offers assisted data interpretation to target the needs of polymer chemists. It facilitates structure characterization, ionization adducts identification, and end- group determination together with visual result reporting. Introduction