Data Set of the paper: Effect of sampling volume on measurements of size and chemical homogeneity of MRI contrast agent FeraSpin™ Rdoi: https://doi.org/10.1039/D5NA00463BAknowledgmentsThe project (22HLT04 MetrINo) has received funding from the European Partnership on Metrology, co-nanced from theEuropean Union's Horizon Europe Research and Innovation Programme and by the Participating States. The authors alsoacknowledge support from the Department of Chemistry of the University of Pavia and from the Ministero dell'Universit`aedella Ricerca (MUR) through the program “Dipartimenti di Eccellenza (2023–2027)”. The authors thank Ute Resch-Genger,Elina Andresen, and Carsten Prinz from BAM for useful discussions. The Cryo-TEM images were obtained at UnitechNOLIMITS, an advanced imaging facility established by the Universit`a degli Studi di Milano. The authors thank Dr DianeBonnet for technical support and valuable inputs on cryo-TEM. This work was funded by the European Association of NationalMetrology Institutes (project number 22HLT04 MetrINo) and by Ministero dell'Istruzione, dell'Universit`a e della Ricerca, “Dipartimenti di Eccellenza (2023–2027)” HTE Lab Chemistry at University of Pavia. The CEA SAXS platform was supported bya France 2030 grant managed by ANR under the reference ANR22-PEXD-0006 in the frame of the PEPR Diadem initiative.