Characterization of polymer-coated CdSe/ZnS quantum dots and investigation of their behaviour in soil solution at relevant concentration by asymmetric flow field-flow fractionation - multi angle light scattering - inductively coupled plasma - mass spectrometry.

A careful separation, identification and characterization of polymer-coated quantum dots (P-QDs) in complex media such as soil solution is the key point to understand their behaviour and to accurately predict their fate in the environment. In the present study, a synthesized CdSe/ZnS core/shell P-QDs suspension, proved to be stable for at least six months, was investigated with respect to P-QDs dimension, structure and elemental composition. Separation of P-QDs and size distribution determination were carried out by Asymmetric Flow Field-Flow Fractionation (AF4) - Multi Angle Light Scattering (MALS). AF4 and MALS were coupled to Inductively Coupled Plasma-Mass Spectrometry (ICPMS) as a selective and sensitive technique for the detection and the characterization of metallic and metalloid analytes. The exploration of element-specific data obtained by ICPMS after AF4 separation enabled the signal to be deconvoluted reliably. Thus, 3 classes of size populations were identified from the whole population of P-QDs. Additionally, a soil solution and a mix of P-QDs suspension with soil solution were characterized by the same method. This strategy enabled the P-QD population, which interacted with the soil solution, to be determined, this interaction leading either to an aggregation or dissolution of the P-QDs. Reproducibility and recovery of the size distributions and element concentrations were examined for each sample. Complementarily, Dynamic Light Scattering (DLS) and Scanning Transmission Electron Microscopy (STEM) were used jointly with AF4-MALS-ICPMS in order to demonstrate all potentialities of this coupling technique.