Characterization of Nanomaterials in Foods

14 Electron microscopy is a recognized standard tool for nanomaterial characterization, and 15 recommended by the European Food Safety Authority for the size measurement of 16 nanomaterials in food. Despite this, little data have been published assessing the reliability of 17 the method, especially for size measurement of nanomaterials characterized by a broad size 18 distribution and/or added to food matrices. This study is a thorough investigation of the 19 measurement uncertainty when applying electron microscopy for size measurement of 20 engineered nanomaterials in foods. Our results show that the number of measured particles 21 was only a minor source of measurement uncertainty for nanomaterials in food, compared to 22