Magnetic in situ determination of surface coordination motifs by utilizing the degree of particle agglomeration

Most analytical techniques used to study the surface chemical properties of superparamagnetic iron oxide nanoparticles (SPIONs) are barely suitable for in situ investigations in liquids, where SPIONs are mostly applied for hyperthermia therapy, diagnostic biosensing, magnetic particle imaging or water purification. Magnetic particle spectroscopy (MPS) can resolve changes in magnetic interactions of SPIONs within seconds at ambient conditions. Herein, we show that by adding mono- and divalent cations to citric acid capped SPIONs, the degree of agglomeration can be utilized to study the selectivity of cations towards surface coordination motifs via MPS. A favored chelate agent, like ethylenediaminetetraacetic acid (EDTA) for divalent cations, removes cations from coordination sites on the SPION surface and causes redispersion of agglomerates. The magnetic determination thereof represents what we call a magnetically indicated complexometric titration. The relevance of

Automated summary

Most analytical techniques for studying the surface chemical properties of SPIONs are not suitable for in situ investigations in liquids. MPS can quickly resolve changes in magnetic interactions of SPIONs at ambient conditions. By adding cations to citric acid capped SPIONs, the degree of agglomeration can be used to study the selectivity of cations towards surface coordination motifs via MPS.