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.
Highlights
Due to an increased use of engineered nanoparticles (ENPs) in a variety of products and applications, the exposure of workers and consumers as well as the release into the environment has to be expected
(1) It has been shown that a direct application of nanoparticle suspensions to an inductively coupled plasma– mass spectrometry (ICP-MS) system does, applying steady state analyses, mostly not provide reliable data for total metal concentrations
Without any further sample preparation, it is very likely that imprecise results and/or instabilities of the measurements occur
Summary
Due to an increased use of engineered nanoparticles (ENPs) in a variety of products and applications, the exposure of workers and consumers as well as the release into the environment has to be expected. To ensure the safety of the different ENPs and to reduce environmental and (eco)toxicological impacts, an appropriate risk assessment and the development of adequate regulatory frameworks are required. This demands for a comprehensive number of scientific studies and for the availability of validated and applicable analytical methods [1,2,3]. These tools should be implementable by non-“nano”-specialized laboratories (e.g., in (eco)toxicological and environmental research or administrative services).
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