Asymmetrical Flow Field Flow Fractionation Coupled to Nanoparticle Tracking Analysis for Rapid Online Characterization of Nanomaterials.

Increasing applications of nanomaterials in consumer goods, industrial products, medical practices, etc., calls for the development of tools for rapid separation, quantification and sizing of nanoparticles to ensure their safe and sustainable employment. While many techniques are available for characterization of pure, homogeneous nanomaterial preparations, particle sizing and counting remains difficult for heterogeneous mixtures resulted from imperfect synthesis conditions, aggregation responsive to change in distribution solutions, or degradation during storage. Herein, nanoparticle tracking analysis (NTA) was coupled to asymmetrical flow field flow fraction (AF4) using a splitter manifold to enable on-line particle separation and counting. The high pressure and flow rate in AF4 were reduced to the levels compatible with NTA by the proper flow splitting design; and a syringe pump was employed to withdrew fluid through the exit port of NTA and maintain consistent flow rates entering NTA for proper particle sizing. Successful AF4-NTA coupling was demonstrated by analyzing a mixture of polystyrene particles with the average diameters around 50, 100, and 200 nm. Good correlation was observed between the amount of each type of particle injected to and measured by the hyphenated system. The particle concentrations acquired using on-line and off-line coupling of AF4-NTA also agreed well with each other. The non-spherical nanoparticles like gold nanorods and hexagonal boron nitride nanosheets were also analyzed to demonstrate the versatile applicability of this system. Our work has proved that, AF4-NTA can achieve accurate particle counting on different populations of the nanomaterials in a mixture, which cannot be done by either AF4 or NTA alone. It will be a valuable tool for rapid characterization of heterogeneous nanomaterial solutions without purification to fulfill the regulation requirement on the nanomaterial-containing products. .