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

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 (pHPZC), which was ∼3.0−3.5 for the studied AgNPs. Addition of salts such as 35 mM NaNO3 or 10 mM Na2S2O3 enhanced the phase separation and thus increased the extraction efficiency of AgNPs. Furthermore, Na2S2O3 efficiently eliminated the interference of Ag+ due to the formation of a complex between Ag+ and S2O32− 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 ...