Metal-engineered nanoparticles (MENPs) with unique optical, electronic, and chemical properties have potential applications in catalysis, optical devices, and electronic applications. Particularly, metallic silver nanoparticles (AgNPs) have been applied as a broadspectrum antimicrobial agent in recent years. Colloidal nanosilver has been used for more than 100 years and has been registered as a biocidal material in the U.S. since 1954.2 AgNPs are the most common materials in nanotechnology-based consumer products, and the worldwide production of AgNPs was estimated at 500 t/a in 2008. 3 Inevitably, these MENPs can be discharged into the environment through the manufacturing, usage, disposal, and recycling processes of commercial products. 4À7The potential toxicity 8 and bioaccumula-
Silver nanoparticles (AgNPs) were selectively concentrated from environmental water samples without disturbing their sizes and shapes by cloud point extraction (CPE) with Triton X-114 (TX-114). The highest extraction efficiency for AgNPs was obtained at about their zero point charge pH (pH PZC ), which was ∼3.0-3.5 for the studied AgNPs. Addition of salts such as 35 mM NaNO 3 or 10 mM Na 2 S 2 O 3 enhanced the phase separation and thus increased the extraction efficiency of AgNPs. Furthermore, Na 2 S 2 O 3 efficiently eliminated the interference of Ag + due to the formation of a complex between Ag + and S 2 O 3 2-that was not extracted into the TX-114-rich phase. The presence of humic acid at an environmentally relevant level (0-30 mg/L dissolved organic carbon) had no effect on the extraction of AgNPs. An enrichment factor of 100 was obtained with 0.2% (w/v) TX-114, and the recoveries of AgNPs from various environmental samples were in the range of 57-116% at 0.1-146 µg/L spiked levels. The AgNPs preconcentrated into the TX-114-rich phase were identified by transmission electron microscopy/scanning electron microscopy-energy dispersive spectrometer/UV-vis spectrum and quantified after microwave digestion by inductively coupled plasma mass spectrometry with a detection limit of 0.006 µg/L (34.3 fmol/L particles of AgNPs). As the proposed CPE procedure preserves the sizes and shapes of AgNPs, the original morphology of AgNPs in environmental waters can be obtained by characterizing the preconcentrated analytes in the TX-114-rich phase. This proposed method provides an efficient approach for the analysis and tracking of AgNPs in the environment.Given their large quantity of production and widespread applications, engineered nanomaterials (NMs) will inevitably be released into the environment during production, handling, and disposal. The unique properties of NMs, such as high surfaceto-volume ratio, mobility and catalytic activity, could cause adverse effects on the eco-environmental system. Evaluation of the risk of NMs to human health and the environment relies on the understanding of their fate, transport, and exposure, as well as their effects on the fate, transport, and exposure of other toxic substances. However, little is known about the occurrence, fate, and toxicity of NMs, partly due to the lack of quantitative methodology for NMs in environmental and biological matrixes. 1-6A variety of methods have been developed for characterization and quantitative analysis of NMs in simple matrixes, as well as natural NMs in a complex matrix such as environmental waters and soils. [7][8][9][10][11][12] Characterization was mainly conducted with microscopy and microscopy-related techniques (e.g., scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM)), whereas quantification was mainly based on the coupling of size separation techniques (e.g., size-exclusion chromatography, 13-15 field flow fractionation, [16][17][18] hydrodynamic chromatography, 19,20 and capill...
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