Optimisation of asymmetrical flow field flow fractionation for environmental nanoparticles separation

The fractionation of natural nanoparticles by Asymmetrical Flow Field Flow Fractionation (As-Fl-FFF) was optimised by considering the following operating conditions: ionic strength, surfactant concentration and crossflow rate. The method performances such as fractionation recovery and fractionation efficiency were evaluated on a stable solution of colloidal-size natural inorganic particles. The online multi-detection by ultraviolet/visible spectrophotometer (UV) and multi-angle laser light scattering (MALLS) provided the monitoring of the sample during the separation and the evaluation of the fractionation efficiency. The lowest ionic strength and surfactant concentrations (i.e. 10−3 mol L−1 NH4NO3 and 3 × 10−4 mol L−1 SDS) allowed to obtain the highest sample recovery and lowest loss of the largest particles. The crossflow rate was investigated in order to avoid significant membrane–sample interaction. The applicability of the fractionation in optimised conditions was evaluated on a natural soil leachate, which was filtrated with different filter cut-offs. Filtration efficiency was stressed by the decrease of the large unfractionated particle influence in the void volume. For the first time, robust operating conditions were proposed to well size-fractionate and characterize soil nanoparticles within a single multi-detection analysis.