On-line determination of soluble Zn content and size of the residual fraction in PM2.5 incubated in various aqueous media

Abstract Transition metals in airborne particulate matter, especially those with aerodynamic diameters no more than 2.5 μm (PM2.5), have attracted considerable attention due to their potential environmental and human health risks. However, determination of these potential risks requires comprehensive knowledge of their dissolution behavior and residual size in aqueous media. Herein, we describe an analytical method for on-line determination of the soluble fraction of Zn as a model transition metal and the size of residual PM2.5 using hollow fiber flow field-flow fractionation (HF5) coupled with UV–vis absorption spectroscopy and inductively coupled plasma optical emission spectroscopy. HF5 was directly applied on the incubated samples in pure water (PW), simulated natural water (SNW), and simulated lung fluid (SLF) due to its efficient in-line filtration and excellent fractionation resolution. Firstly, the potential of the proposed method (under optimized conditions) for size characterization was assessed against commercial silica microparticles, and results in good agreement with manufacturer and scanning electron microscopy values were obtained. The accuracy of quantification of soluble Zn in various media was then validated using a standard reference material in terms of satisfactory recoveries compared with the reference values. For the real PM2.5 samples collected from different sites in Beijing, China, the soluble Zn percentages in PW, SNW, and SLF were within 15.4–16.7%, 10.6–12.7%, and 43.1–46.9%, respectively, with the amount of particles smaller than ~10 nm released from PM2.5 increasing in the order of SNW