Seawater analysis of engineered nanoparticles using ICP-MS-based technology: Addressing challenges with the...

With an increasing production and use of engineered nanoparticles (ENPs), inevitably grows their release into the environment. This makes it important to determine in what quantitates they occur in aquatic systems like seawater. However, even when using the most sensitive ICP-MS technique, quantification of very low seawater concentrations of ENPs is still concept rather than the fact. To approach this goal, a unified protocol for the preparation of seawater samples for ICP-MS analysis has been developed in this study using a selection of silver, titanium dioxide and zinc oxide nanoparticles. In order to minimize the risk of particle loss, the effect of sample pH was examined and it was found out that a moderate in-field acidification (to pH 7.5) ensures particle stability prior to analysis. Ultrafiltration through commercial 3 kDa membrane filters was shown feasible to separate the ENPs from the bulk seawater sample provided that the filter unit is pre-conditioned with 0.1 M copper nitrate to avoid ionic metal adsorption. The following ultrasound-mediated dissolution in 30% HNO₃ directly in the filer unit and ultrafiltration makes the metals constituting the ENPs amenable to analysis. The latter was for the first time performed using high-resolution ICP-MS method validated according to the common EU standards. The limits of detection attained here were as low as 0.06, 0.09, and 17.5 μg L^-1 for Ag, TiO₂, and ZnO nanoparticles, respectively. Accuracy of the method was tested with uncontaminated open-sea water spiked with ENPs and recoveries were acceptable ranging from 85 to 110%.