ICP-MS-based characterization of inorganic nanoparticles—sample preparation and off-line fractionation strategies

Abstract

Validated and easily applicable analytical tools are required to develop and implement regulatory frameworks and an appropriate risk assessment for engineered nanoparticles (ENPs). Concerning metal-based ENPs, two main aspects are the quantification of the absolute mass concentration and of the “dissolved” fraction in, e.g., (eco)toxicity and environmental studies. To provide information on preparative aspects and on potential uncertainties, preferably simple off-line methods were compared to determine (1) the total concentration of suspensions of five metal-based ENP materials (Ag, TiO2, CeO2, ZnO, and Au; two sizes), and (2) six methods to quantify the “dissolved” fraction of an Ag ENP suspension. Focusing on inductively coupled plasma–mass spectrometry, the total concentration of the ENP suspensions was determined by direct measurement, after acidification and after microwave-assisted digestion. Except for Au 10 nm, the total concentrations determined by direct measurements were clearly lower than those measured after digestion (between 61.1 % for Au 200 nm and 93.7 % for ZnO). In general, acidified suspensions delivered better recoveries from 89.3 % (ZnO) to 99.3 % (Ag). For the quantification of dissolved fractions two filtration methods (ultrafiltration and tangential flow filtration), centrifugation and ion selective electrode were mainly appropriate with certain limitations, while dialysis and cloud point extraction cannot be recommended. With respect to precision, time consumption, applicability, as well as to economic demands, ultrafiltration in combination with microwave digestion was identified as best practice.FigureA Multi-method approach to identify best practice for ICP-MS based off-line characterization of ENP suspensions.Electronic supplementary materialThe online version of this article (doi:10.1007/s00216-013-7480-2) contains supplementary material, which is available to authorized users.

Measurement and characterization of engineered titanium dioxide nanoparticles in the environment

“…Previous researchers already reviewed methods to characterize and measure ENPs in the environment (Tiede et al, 2008;Hassellöv et al, 2008;Stone et al, 2010;Silva et al, 2011;Tsao et al, 2011;Weir et al, 2012;Xiao and Wiesner, 2012;Zänker and Schierz, Gottschalk et al, 2013;Luo et al, 2013;Fabricius et al, 2014). Herein, a short overview is given on methods that may be used to study engineered TiO 2 -NPs.…”

“…Herein, a short overview is given on methods that may be used to study engineered TiO 2 -NPs. For a detailed description of these methods, we refer to the specific literature (Tiede et al, 2008;Stone et al, 2010;Zänker and Schierz, 2012;Fabricius et al, 2014). We focus on discussing the advantages and disadvantages of these methods, and possible drawbacks to be taken into account when using these techniques to study engineered TiO 2 -NPs.…”

“…In spite of having relatively cumbersome and complicated features, FFF is probably the most promising fractionation technique for TiO 2 -NPs. Similarly, the other separation methods, like manipulation between solvent phases (e.g., cloud point extraction and CE), experience problems, such as being very time-consuming, possessing methodological, and handling difficulties, as well as elevated costs (Fabricius et al, 2014). Therefore, an easy to handle, sufficiently available, and moderately expensive tool is needed to separate TiO 2 -NPs.…”

“…An ATOF-MS consists of an aerosol introduction interface; a light-scattering region for sizing and a TOF-MS (time-of-flight mass spectrometer). MS approaches nowadays have been widely applied to measure NPs in the environment (Gray et al, 2012;Liu et al, 2012;Fabricius et al, 2014).…”

“…Therefore, validation of analytical methods appropriate for ENPs is challenging, particularly in different matrixes, and multi-method approaches are often required to provide reliable data as well as to assess and control the limitations of different techniques. This demands that there is not only a comprehensive number of cross-scientific studies but also availability of validated and easily applicable analytical methods (Fabricius et al, 2014).…”