Cloud Point Extraction as an Advantageous Preconcentration Approach for Analysis of Trace Silver Nanoparticles in Environmental Waters

Abstract

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.