Fractionation and preconcentration of silver nanoparticles at environmentally relevant concentrations through induced eco-corona formation and spICP-MS characterization

Abstract

The increasing application of nanoparticles (NPs) to different products by the industry has raised concerns regarding their release into environmental matrices. Single-particle inductively coupled plasma mass spectrometry (spICP-MS) is a growing technique based on counting particle events that allow the characterisation and quantification of NPs at environmental concentrations. However, a number concentration (N_NP) of 10⁴–10⁵ NPs per mL in the suspension is required. Considering 10 ng L⁻¹ for 80 nm AgNPs, a N_NP of ∼3500 NPs per mL is expected; thus, a preconcentration step can be an alternative to increase the N_NP. Eco-corona formation with humic acid (HA) and NPs is a well-known environmental process. This work used an induced eco-corona formation to fractionate and preconcentrate NPs in environmental waters. For ultrapure water, 7 times more NPs were detected in the spICP-MS analysis, representing a N_NP of ∼2.9 × 10⁴ NPs per mL, with a concentration factor (CF) ∼9 times that for both N_NP and mass concentration (∼80 ng L⁻¹). Additionally, the size of the AgNPs was maintained after the method without compromising NP characterisation. The method's feasibility was also tested in drinking water, tap water, and river water, and a CF between 7 and 8 times that for N_NP and mass concentration was obtained, demonstrating its applicability despite the matrix composition and pH. The induced eco-corona method can be used to track NPs in environmental waters at concentrations <10 ng L⁻¹; besides the main objective of preconcentrating NPs, making the samples suitable for analysis by spICP-MS was achieved, allowing the NPs' proper size distribution characterization according to spICP-MS theory.