Sample preparation for the analysis of nanoparticles in natural waters by single particle ICP-MS

With the significant increase in the production and use of nanoparticles (NP), concern is increasing over their release into their environment. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is emerging as one of the best techniques for detecting the very small NP at very low concentrations in natural waters. However, there is no unified protocol for the preparation of natural water samples for SP-ICP-MS analysis. In order to minimize nebulizer blockage, filtration is often used with the expectation that 0.45 μm membranes will not remove significant quantities of 1-100 nm NP. Nonetheless, there are limited data on its effect on the concentrations or size distributions of the NP. To that end, we examined the interactions between six different membrane filters and silver (Ag) and cerium oxide (CeO₂) NP in aqueous samples. For Ag NP, the highest recoveries were observed for polypropylene membranes, where 55% of the pre-filtration NP were found in rainwater and 75% were found in river waters. For CeO₂ NP, recoveries for the polypropylene membrane attained 60% in rainwater and 75% in river water. Recoveries could be increased to over 80% by pre-conditioning the filtration membranes with a multi-element solution. Similar recoveries were obtained when samples were centrifuged at low centrifugal forces (≤1000×g).

Quantification and Characterization of Ti-, Ce-, and Ag-Nanoparticles in Global Surface Waters and Precipitation

Nanoparticle (NP) emissions to the environment are increasing as a result of anthropogenic activities, prompting concerns for ecosystems and human health. In order to evaluate the risk of NPs, it is necessary to know their concentrations in various environmental compartments on regional and global scales; however, these data have remained largely elusive due to the analytical difficulties of measuring NPs in complex natural matrices. Here, we measure NP concentrations and sizes for Ti-, Ce-, and Ag-containing NPs in numerous global surface waters and precipitation samples, and we provide insights into their compositions and origins (natural or anthropogenic). The results link NP occurrences and distributions to particle type, origin, and sampling location. Based on measurements from 46 sites across 13 countries, total Ti- and Ce-NP concentrations (regardless of origin) were often found to be within 10⁴ to 10⁷ NP mL^-1, whereas Ag NPs exhibited sporadic occurrences with low concentrations generally up to 10⁵ NP mL^-1. This generally corresponded to mass concentrations of <1 ng L^-1 for Ag-NPs, <100 ng L^-1 for Ce-NPs, and <10 μg L^-1 for Ti-NPs, given that measured sizes were often below 15 nm for Ce- and Ag-NPs and above 30 nm for Ti-NPs. In view of current toxicological data, the observed NP levels do not yet appear to exceed toxicity thresholds for the environment or human health; however, NPs of likely anthropogenic origins appear to be already substantial in certain areas, such as urban centers. This work lays the foundation for broader experimental NP surveys, which will be critical for reliable NP risk assessments and the regulation of nano-enabled products.

Measurement of CeO2 Nanoparticles in Natural Waters Using a High Sensitivity, Single Particle ICP-MS

As the production and use of cerium oxide nanoparticles (CeO₂ NPs) increases, so does the concern of the scientific community over their release into the environment. Single particle inductively coupled plasma mass spectrometry is emerging as one of the best techniques for NP detection and quantification; however, it is often limited by high size detection limits (SDL). To that end, a high sensitivity sector field ICP-MS (SF-ICP-MS) with microsecond dwell times (50 µs) was used to lower the SDL of CeO₂ NPs to below 4.0 nm. Ag and Au NPs were also analyzed for reference. SF-ICP-MS was then used to detect CeO₂ NPs in a Montreal rainwater at a concentration of (2.2 ± 0.1) × 10⁸ L⁻¹ with a mean diameter of 10.8 ± 0.2 nm; and in a St. Lawrence River water at a concentration of ((1.6 ± 0.3) × 10⁹ L⁻¹) with a higher mean diameter (21.9 ± 0.8 nm). SF-ICP-MS and single particle time of flight ICP-MS on Ce and La indicated that 36% of the Ce-containing NPs detected in Montreal rainwater were engineered Ce NPs.

Lowering the Size Detection Limits of Ag and TiO2 Nanoparticles by Single Particle ICP-MS

As the production and use of engineered nanomaterials increase, there is an urgent need to develop analytical techniques that are sufficiently sensitive to be able to measure the very small nanoparticles (NP) at very low concentrations. Although single particle ICP-MS (SP-ICP-MS) is emerging as one of the best techniques for detecting NP, it is limited by relatively high size detection limits for several NP, including many of the oxides. The use of a high sensitivity sector field ICP-MS (ICP-SF-MS), microsecond dwell times, and dry aerosol sample introduction systems were examined with the goal of lowering the size detection limits of the technique. For samples injected as a wet aerosol, size detection limits as low as 4.9 nm for Ag NP and 19.2 nm for TiO₂ NP were determined. By using a dry aerosol, a significant gain in ion extraction from the plasma was obtained, which resulted in a noticeable decrease of the size detection limits to 3.5 nm for the Ag NP and 12.1 nm for the TiO₂ NP. These substantial improvements were applied to the detection of TiO₂ NP in sunscreen lotions, rainwaters, and swimming pool waters. Concentrations of Ti-containing NP between 27 and 193 μL^-1 were found in rain samples. Similar NP concentrations were detected in public swimming pools, although much higher particle number concentrations (6046 ± 290 μL^-1) were measured in a paddling pool, which was attributed to a high concentration of sunscreen lotions in a small recirculated water volume. High losses of TiO₂ NP through adsorption or agglomeration resulted in recoveries ranging from 14-34%.