Quantitatively, the particles were thermogravimetrically analyzed with a TG 209 F1 Libra from Netzsch. The temperature was continuously increased to 1000 °C at 30 °C min -1 while being exposed to a gas flow of 10 mL min -1 of O2 and 40 mL min -1 of N2. The measured curves were smoothed with the software Netzsch Proteus Thermal Analysis 8.0.3. The grafting densities of the phosphonic acids (GDPA) on the SPIONs' surface were estimated via Equation 1. wt is the relative mass loss between 150 and 700 °C in percent, NA is Avogadro's constant, MWPA is the molar mass of the respective phosphonic acid derivate (or of PAC16/PAC10Ph respectively for the binary coated SPIONs as they make up the majority of the coating as determined by ATR-FTIR) corrected by the staying anchor group and SSASPIONs the specific surface area of the SPIONs.