Optimisation, evaluation and application of asymmetrical flow field-flow fractionation with single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) to characterise silver nanoparticles in environmental media

• The performance of asymmetric flow field-flow fractionation (AF4) on silver nanoparticle (AgNP) separation were assessed.
• Operational conditions of AF4 were optimized for the separation of polyvinylpyrrolidone (PVP)- and citrate-coated AgNPs.
• Erroneous and biased interpretation of AF4 performance was avoided by comparing the results between diverse detectors.
• The proposed methodology was applied to real environmental media to verify its practicality.

The consumption of nanomaterials has been steadily increasing in various industrial and commercial sectors. For engineered nanoparticles (ENPs), the development of appropriate methods for separating, characterising and quantifying is a prerequisite for their risk assessment and evaluation in terms of environmental exposure. Asymmetrical flow field-flow fractionation (AF4) coupled with single particle inductively coupled plasma mass spectrometry (AF4/SP-ICP-MS) is considered to be a valuable tool able to achieve these goals. Studies on the evaluation of AF4 performance, however, are lacking because most previous research has considered the separation and quantification of ENPs separately without verifying the resolution and recovery regarding AF4. As a result, a biased and erroneous interpretation of AF4 capability could result. Moreover, focus has been on the characterisation of individual ENPs, although various properties of ENPs, such as the type of capping materials, greatly affect the performance of AF4. For this reason, this study focused on the optimisation of AF4 operational conditions by considering the effects of coating materials to efficiently separate silver NPs (AgNPs). In addition, the overall performance of AF4 was evaluated by comparing results obtained from various detectors, such as ultraviolet-visible spectroscopy (UV–VIS), multi-angle light scattering (MALS), dynamic light scattering (DLS), transmission electron microscopy (TEM) and SP-ICP-MS. A methodology was proposed to correct the erroneous and biased interpretation of AF4 performance in terms of signal characteristics, resolution and recovery. Then, the optimised method was applied to real aqueous samples to verify its practicality on environmental media.