Natural England 1 article published in JoVE Engineering UV-Vis Spectroscopic Characterization of Nanomaterials in Aqueous Media Ana C. Quevedo1, Emily Guggenheim1, Sophie M. Briffa1, Jessica Adams2,3, Stephen Lofts2, Minjeong Kwak4, Tae Geol Lee4, Colin Johnston5, Stephan Wagner6, Timothy R. Holbrook6, Yves U. Hachenberger7, Jutta Tentschert7, Nicholas Davidson1, Eugenia Valsami-Jones1 1School of Geography, Earth and Environmental Sciences, University of Birmingham, 2UK Centre for Ecology and Hydrology, 3Natural England, 4Center for Nanosafety Metrology, Korea Research Institute of Standards and Science (KRISS), 5Department of Materials, University of Oxford, 6Department of Analytical Chemistry, Helmholtz-Centre for Environmental Research, 7Department of Chemical and Product Safety, German Federal Institute for Risk Assessment (BfR) This study presents the benchmarking results for an interlaboratory comparison (ILC) designed to test the standard operating procedure (SOP) developed for gold (Au) colloid dispersions characterized by ultraviolet-visible Spectroscopy (UV-Vis), amongst six partners from the H2020 ACEnano project for sample preparation, measurement, and analysis of the results.