title: Optimization and evaluation of asymmetric flow field-flow fractionation of silver nanoparticles.
abstract: Asymmetric flow field-flow fractionation (AF(4)) in combination with on-line optical detection and mass spectrometry is one of the most promising methods for separation and quantification of nanoparticles (NPs) in complex matrices including food. However, to obtain meaningful results regarding especially the NP size distribution a number of parameters influencing the separation need to be optimized. This paper describes the development of a separation method for polyvinylpyrrolidone-stabilized silver nanoparticles (AgNPs) in aqueous suspension. Carrier liquid composition, membrane material, cross flow rate and spacer height were shown to have a significant influence on the recoveries and retention times of the nanoparticles. Focus time and focus flow rate were optimized with regard to minimum elution of AgNPs in the void volume. The developed method was successfully tested for injected masses of AgNPs from 0.2 to 5.0 μg. The on-line combination of AF(4) with detection methods including ICP-MS, light absorbance and light scattering was helpful because each detector provided different types of information about the eluting NP fraction. Differences in the time-resolved appearance of the signals obtained by the three detection methods were explained based on the physical origin of the signal. Two different approaches for conversion of retention times of AgNPs to their corresponding sizes and size distributions were tested and compared, namely size calibration with polystyrene nanoparticles (PSNPs) and calculations of size based on AF(4) theory. Fraction collection followed by transmission electron microscopy was performed to confirm the obtained size distributions and to obtain further information regarding the AgNP shape. Characteristics of the absorbance spectra were used to confirm the presence of non-spherical AgNP.
authors.affiliation: Division of Food Chemistry, National Food Institute, Technical University of Denmark, Mørkhøj Bygade 19, DK-2860 Søborg, Denmark.
authors.forename: Katrin
authors.initials: K
authors.lastname: Loeschner
authors.forename: Jana
authors.initials: J
authors.lastname: Navratilova
authors.forename: Samuel
authors.initials: S
authors.lastname: Legros
authors.forename: Stephan
authors.initials: S
authors.lastname: Wagner
authors.forename: Ringo
authors.initials: R
authors.lastname: Grombe
authors.forename: James
authors.initials: J
authors.lastname: Snell
authors.forename: Frank
authors.initials: F
authors.lastname: von der Kammer
authors.forename: Erik H
authors.initials: EH
authors.lastname: Larsen
mesh_terms: D031521:Fractionation, Field Flow / Q000379:methods*; D008027:Light; D053768:Metal Nanoparticles / Q000032:analysis* / Q000648:ultrastructure; D010316:Particle Size; D012212:Rheology; D012542:Scattering, Radiation; D012834:Silver / Q000032:analysis*; D013054:Spectrophotometry, Atomic; D013535:Suspensions; D013997:Time Factors
chemical_list: D013535:Suspensions; D012834:Silver