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

Abstract

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%.

Characterization of TiO2 NPs in Radish (Raphanus sativus L.) by Single-Particle ICP-QQQ-MS

“…In comparison with studies performed by high-resolution (HR) ICP-MS (Tharaud et al, 2017), the current study presented a slightly higher LOD size in ultrapure water (15 nm vs. 10 nm by HR-ICP-MS) but a significant improvement when analyzing TiO 2 NPs in a matrix containing 50 mg L −1 of Ca (21 nm vs. 37 nm by HR-ICP-MS). Finally, the size detection limits obtained here by single-particle QQQ-ICP-MS in MS/MS mode were at similar levels than those reported by using double-focusing magnetic sector field ICP-MS (ICP-SF-MS): 19.2 nm for samples injected as a wet aerosol (Hadioui et al, 2019) and 20 nm for TiO 2 NPs the snow and rain waters (Azimzada et al, 2020).…”

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

“…Peaks were considered if their intensity was greater than the average background + three times the standard deviation of the background. SF-ICP-MS data were processed using Nu Quant software (version 2.2, Nu Instruments, Wrexham, UK [18,39]). A built-in algorithm searches in a fixed window (3-15 ms) for a peak maximum that is greater than the signal of the smoothed background.…”

“…Size detection limits (nm) are determined from the threshold intensity (I T ) (counts) used to discriminate between NP and the background according to Equation (1) [15,18].…”

“…The minimal particle size (size detection limit = SDL) that can be measured by SP-ICP-MS depends largely upon the signal to noise ratio. A number of approaches have been employed to decrease the SDL [18] including: sample dilution, judicious choice of isotopes, interference removal strategies [19,20], shorter dwell times [21], etc.…”

Anthropogenic Release and Distribution of Titanium Dioxide Particles in a River Downstream of a Nanomaterial Manufacturer Industrial Site

“…For example, three different sampling campaigns that analyzed filtered waters (<0.45 µm) near a wastewater treatment plant (WWTP) confirmed TiO 2 NM presence with electron microscopy and reported Ti values between 0.7 and 3 µg/L (Johnson et al, 2011;de Klein et al, 2016;Markus et al, 2018). Single particle (SP)-ICP-MS was utilized to target and detect smaller TiO 2 particles down to 100 nm in river surface waters without the need for filtration (Peters et al, 2018), and Hadioui et al (2019) have now detected TiO 2 particle sizes down to 19.2 nm with the technique. While progress has been made in detecting low concentrations of TiO 2 NMs (µg/L) in complex environmental matrices, these analyses alone cannot confirm that the particles are anthropogenic.…”