A protocol for size-based measurements of nanoplastics across the range 20 nm - 200 nm

The on-line coupling of asymmetric flow field-flow fractionation (AF4-FFF) to multi-angle light scattering (MALS) and UV diode array (UV-DAD) detectors to simultaneously separate, collect information about the size and quantify the polystyrene nanoplastics (PS-NPs) was tested. A mixture of PS-NPs with nominal size of 20±2 nm, 60±4 nm, 100±3 nm and 200±5 nm was prepared by dilution with ultrapure deionized water and gentle mixing. From the AF4- FFF results, the smaller nanoplastics (20 nm) had a dominant peak at short elution time while the larger ones (200 nm) had the dominant peak at high elution time, and nanoplastics at 60 nm and 100 nm eluted in the middle region. From MALS analysis using the 90° scattering angle, the obtained size of the different peaks was consistent with the values provided by the supplier. By UV-DAD detection, concentrations of the nanoplastic populations were measured at the wavelength of 215 nm. The power of AF4-FFF resides in its essential tunability: simply by changing flow rates, a single separation channel can be used to explore complex samples across the size range 20 nm-200 nm, with high resolution between differently sized nanoplastics, and providing the possibility to identify sample components through coupling to on-line detectors.