The quantification and characterization of natural, engineered, and incidental nano- to micro-size particles are beneficial to assessing a nanomaterial’s performance in manufacturing, their fate and ...transport in the environment, and their potential risk to human health. Single particle inductively coupled plasma mass spectrometry (spICP-MS) can sensitively quantify the amount and size distribution of metallic nanoparticles suspended in aqueous matrices. To accurately obtain the nanoparticle size distribution, it is critical to have knowledge of the size detection limit (denoted as D min) using spICP-MS for a wide range of elements (other than a few available assessed ones) that have been or will be synthesized into engineered nanoparticles. Herein is described a method to estimate the size detection limit using spICP-MS and then apply it to nanoparticles composed of 40 different elements. The calculated D min values correspond well for a few of the elements with their detectable sizes that are available in the literature. Assuming each nanoparticle sample is composed of one element, D min values vary substantially among the 40 elements: Ta, U, Ir, Rh, Th, Ce, and Hf showed the lowest D min values, ≤10 nm; Bi, W, In, Pb, Pt, Ag, Au, Tl, Pd, Y, Ru, Cd, and Sb had D min in the range of 11–20 nm; D min values of Co, Sr, Sn, Zr, Ba, Te, Mo, Ni, V, Cu, Cr, Mg, Zn, Fe, Al, Li, and Ti were located at 21–80 nm; and Se, Ca, and Si showed high D min values, greater than 200 nm. A range of parameters that influence the D min, such as instrument sensitivity, nanoparticle density, and background noise, is demonstrated. It is observed that, when the background noise is low, the instrument sensitivity and nanoparticle density dominate the D min significantly. Approaches for reducing the D min, e.g., collision cell technology (CCT) and analyte isotope selection, are also discussed. To validate the D min estimation approach, size distributions for three engineered nanoparticle samples were obtained using spICP-MS. The use of this methodology confirms that the observed minimum detectable sizes are consistent with the calculated D min values. Overall, this work identifies the elements and nanoparticles to which current spICP-MS approaches can be applied, in order to enable quantification of very small nanoparticles at low concentrations in aqueous media.
From its early beginnings in characterizing aerosol particles to its recent applications for investigating natural waters and waste streams, single particle inductively coupled plasma-mass ...spectrometry (spICP-MS) has proven to be a powerful technique for the detection and characterization of aqueous dispersions of metal-containing nanomaterials. Combining the high-throughput of an ensemble technique with the specificity of a single particle counting technique and the elemental specificity of ICP-MS, spICP-MS is capable of rapidly providing researchers with information pertaining to size, size distribution, particle number concentration, and major elemental composition with minimal sample perturbation. Recently, advances in data acquisition, signal processing, and the implementation of alternative mass analyzers (e.g., time-of-flight) has resulted in a wider breadth of particle analyses and made significant progress toward overcoming many of the challenges in the quantitative analysis of nanoparticles. This review provides an overview of spICP-MS development from a niche technique to application for routine analysis, a discussion of the key issues for quantitative analysis, and examples of its further advancement for analysis of increasingly complex environmental and biological samples.
Graphical Abstract
Single particle ICP-MS workflow for the analysis of suspended nanoparticles
Environmental risk assessments of engineered nanoparticles require thorough characterization of nanoparticles and their aggregates. Furthermore, quantitative analytical methods are required to ...determine environmental concentrations and enable both effect and exposure assessments. Many methods still need optimization and development, especially for new types of nanoparticles in water, but extensive experience can be gained from the fields of environmental chemistry of natural nanomaterials and from fundamental colloid chemistry. This review briefly describes most methods that are being exploited in nanoecotoxicology for analysis and characterization of nanomaterials. Methodological aspects are discussed in relation to the fields of nanometrology, particle size analysis and analytical chemistry. Differences in both the type of size measures (length, radius, aspect ratio, etc.), and the type of average or distributions afforded by the specific measures are compared. The strengths of single particle methods, such as electron microscopy and atomic force microscopy, with respect to imaging, shape determinations and application to particle process studies are discussed, together with their limitations in terms of counting statistics and sample preparation. Methods based on the measurement of particle populations are discussed in terms of their quantitative analyses, but the necessity of knowing their limitations in size range and concentration range is also considered. The advantage of combining complementary methods is highlighted.
Currently there are few ideal methods for the characterization of nanoparticles in complex, environmental samples, leading to significant gaps in toxicity and exposure assessments of nanomaterials. ...Single particle-inductively coupled plasma-mass spectrometry (spICPMS) is an emerging technique that can both size and count metal-containing nanoparticles. A major benefit of the spICPMS method is its ability to characterize nanoparticles at concentrations relevant to the environment. This paper presents a practical guide on how to count and size nanoparticles using spICPMS. Different methods are investigated for measuring transport efficiency (i.e., nebulization efficiency), an important term in the spICPMS calculations. In addition, an alternative protocol is provided for determining particle size that broadens the applicability of the technique to all types of inorganic nanoparticles. Initial comparison, using well-characterized, monodisperse silver nanoparticles, showed the importance of having an accurate transport efficiency value when determining particle number concentration and, if using the newly presented protocol, particle size. Ultimately, the goal of this paper is to provide improvements to nanometrology by further developing this technique for the characterization of metal-containing nanoparticles.
Expanded use of engineered nanoparticles (ENPs) in consumer products increases the potential for environmental release and unintended biological exposures. As a result, measurement techniques are ...needed to accurately quantify ENP size, mass, and particle number distributions in biological matrices. This work combines single particle inductively coupled plasma mass spectrometry (spICPMS) with tissue extraction to quantify and characterize metallic ENPs in environmentally relevant biological tissues for the first time. ENPs were extracted from tissues via alkaline digestion using tetramethylammonium hydroxide (TMAH). Method development was performed using ground beef and was verified in Daphnia magna and Lumbriculus variegatus. ENPs investigated include 100 and 60 nm Au and Ag stabilized by polyvynylpyrrolidone (PVP). Mass- and number-based recovery of spiked Au and Ag ENPs was high (83–121%) from all tissues tested. Additional experiments suggested ENP mixtures (60 and 100 nm Ag ENPs) could be extracted and quantitatively analyzed. Biological exposures were also conducted to verify the applicability of the method for aquatic organisms. Size distributions and particle number concentrations were determined for ENPs extracted from D. magna exposed to 98 μg/L 100 nm Au and 4.8 μg/L 100 nm Ag ENPs. The D. magna nanoparticulate body burden for Au ENP uptake was 613 ± 230 μg/kgww, while the measured nanoparticulate body burden for D. magna exposed to Ag ENPs was 59 ± 52 μg/kgww. Notably, the particle size distributions determined from D. magna tissues suggested minimal shifts in the size distributions of ENPs accumulated, as compared to the exposure media.
Sizing engineered nanoparticles in simple, laboratory systems is now a robust field of science; however, application of available techniques to more complex, natural systems is hindered by numerous ...challenges including low nanoparticle number concentrations, polydispersity from aggregation and/or dissolution, and interference from other incidental particulates. A new emerging technique, single particle inductively coupled plasma-mass spectrometry (spICPMS), has the potential to address many of these analytical challenges when sizing inorganic nanoparticles in environmental matrices. However, to date, there is little beyond the initial feasibility studies that investigates the performance characteristics and validation of spICPMS as a nanoparticle sizing technique. This study compares sizing of four silver nanoparticle dispersions (nominal diameters of 40, 60, 80, and 100 nm) by spICPMS to four established sizing techniques: dynamic light scattering, differential centrifugal sedimentation, nanoparticle tracking analysis, and TEM. Results show that spICPMS is able to size silver nanoparticles, across different sizes and particle number concentrations, with accuracy similar to the other commercially available techniques. Furthermore, a novel approach to evaluating particle coincidence is presented. In addition, spICPMS size measurements were successfully performed on nanoparticles suspended in algal growth media at low concentrations. Overall, while further development of the technique is needed, spICPMS yields important advantages over other techniques when sizing nanoparticles in environmentally relevant media.
Monitoring data are necessary for the future production of engineered nanomaterials and the development of regulations for nanomaterials. Therefore, it is necessary to develop methods that reliably ...detect and quantify nanomaterials in real-world systems at expectedly low concentrations. In this work we tested several methodological approaches to detect titanium dioxide nanomaterials released from sunscreen products into the Old Danube Lake (Vienna, Austria), which is heavily used for recreational activities like bathing and water sports during the summer season. During a 12-month period suspended particulate matter (SPM) was collected from the lake and analyzed using a combination of complementary techniques. By sampling at a location approximately 50 m from the nearest bathing area and at one meter depth from the water surface, we focused on the potentially mobile fraction of the released nanoparticles. We were able to identify titanium dioxide nanoparticles stemming from sunscreens in the suspended matter of the lake using electron microscopy. Bulk analysis of SPM clearly shows an increase of Ti-containing particles during the summer season. These analyses, however, are not able to distinguish sunscreen nanoparticles from natural Ti-bearing nanoparticles. Therefore, Elemental ratios of Ti with Al, V, Ga, Y, Nb, Eu, Ho, Er, Tm, Yb, and Ta as determined by ICPMS and ICPOES, in combination with single particle ICPMS analysis were applied to establish local background values. The observed mild increase of Ti elemental ratios, compared to spring background values indicates that the residence time of released nanomaterials in the water column is rather short. Overall, the advantages and disadvantages of the methods used to detect and characterize the nanomaterials are discussed.
Wildfires at the wildland–urban interface (WUI) are increasing in frequency and intensity, driven by climate change and anthropogenic ignitions. Few studies have characterized the variability in the ...metal content in ash generated from burned structures in order to determine the potential risk to human and environmental health. Using inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS), we analyzed leachable trace metal concentration in soils and ash from structures burned by the Marshall Fire, a WUI fire that destroyed over 1000 structures in Boulder County, Colorado. Acid digestion revealed that ash derived from structures contained 22 times more Cu and 3 times more Pb on average than surrounding soils on a mg/kg basis. Ash liberated 12 times more Ni (mg/kg) and twice as much Cr (mg/kg) as soils in a water leach. By comparing the amount of acid-extractable metals to that released by water and simulated epithelial lung fluid (SELF), we estimated their potential for environmental mobility and human bioaccessibility. The SELF leach showed that Cu and Ni were more bioaccessible (mg of leachable metal/mg of acid-extractable metal) in ash than in soils. These results suggest that structure ash is an important source of trace metals that can negatively impact the health of both humans and the environment.
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