title: In situ analysis of a bimodal size distribution of superparamagnetic nanoparticles.
abstract: The dispersed iron oxide nanoparticles of ferrofluids in aqueous solution are difficult to characterize due to their protective polymer coatings. We report on the bimodal size distribution of superparamagnetic iron oxide nanoparticles found in the MRI contrast agent Resovist, which is a representative example of commercial nanoparticle-based pharmaceutical formulations. The radii of the majority of the nanoparticles (>99%) range from 4 to 13 nm (less than 1% of the particles display radii up to 21 nm). The maxima of the size distributions are at 5.0 and 9.9 nm. The analysis was performed with in situ characterization of Resovist via online coupling of asymmetrical flow field-flow fractionation (A4F) with small-angle X-ray scattering (SAXS) using a standard copper X-ray tube as a radiation source. The outlet of the A4F was directly coupled to a flow capillary on the SAXS instrument. SAXS curves of nanoparticle fractions were recorded at 1-min time intervals. We recommend using the A4F-SAXS coupling as a routine method for analysis of dispersed nanoparticles with sizes in the range of 1-100 nm. It allows a fast and quantitative comparison of different batches without the need for sample preparation.
authors.affiliation: BAM Federal Institute for Materials Research and Testing, Richard-Willstatter-Strabetae 11, 12489 Berlin, Germany. andreas.thuenemann@bam.de
authors.forename: Andreas F
authors.initials: AF
authors.lastname: Thünemann
authors.forename: Simone
authors.initials: S
authors.lastname: Rolf
authors.forename: Patrick
authors.initials: P
authors.lastname: Knappe
authors.forename: Steffen
authors.initials: S
authors.lastname: Weidner
mesh_terms: D003287:Contrast Media / Q000737:chemistry*; D003911:Dextrans; D005290:Ferric Compounds / Q000737:chemistry*; D052203:Ferrosoferric Oxide; D007501:Iron / Q000737:chemistry*; D008280:Magnetics / Q000379:methods*; D058185:Magnetite Nanoparticles; D053758:Nanoparticles / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D053838:Scattering, Small Angle; D013056:Spectrophotometry, Ultraviolet; D014961:X-Ray Diffraction
chemical_list: D003287:Contrast Media; D003911:Dextrans; D005290:Ferric Compounds; D058185:Magnetite Nanoparticles; D010087:Oxides; C000499:ferric oxide; D007501:Iron; C065507:ferumoxides; D052203:Ferrosoferric Oxide