Speciation Analysis of Ag2S and ZnS Nanoparticles at the ng/L Level in Environmental Waters by Cloud Point Extraction Coupled with LC-ICPMS.

Toxicity and transport of metal-based nanoparticles (M-NPs) in environmental waters strongly depend on their speciation. A detailed understanding of the composition and speciation of M-NPs is necessary in order to move this field forward. Unfortunately, there is a shortage of analytical methods for metal-sulfide nanoparticles (MS-NPs) in the environment. In this work, a cloud point extraction (CPE) method combined with liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (LC-ICPMS) is developed for sensitive determination of Ag2S- and ZnS-NPs. Under the condition of 0.15% (w/v) of Triton X-114 (TX-114), pH 5, 20 mM NaNO3, incubation temperature of 45 °C, and time of 15 min, MS-NPs and non-MS-NPs were extracted into the surfactant-rich phase. With the sequent addition of 10 mM bis(p-sulfonatophenyl)phenylphosphane dehydrate dipotassium (BSPP) aqueous solution (100 μL) into the CPE-obtained extract, the non-MS-NPs were selectively dissociated into their ionic counterparts while maintaining the original size and shape of Ag2S- and ZnS-NPs. Interestingly, the micelle-mediated behavior suddenly disappeared with the addition of BSPP. Thus, the extract can be injected to LC-ICPMS for speciation analysis of trace Ag2S- and ZnS-NPs. This method exhibited excellent reproducibility (relative standard deviations < 4.9%), high sensitivity with the respective detection limits of 8 ng/L for Ag2S-NPs and 15 ng/L for ZnS-NPs, enabling recoveries of 81.3-96.6% for Ag2S-NPs and 83.9-93.5% for ZnS-NPs when they were spiked into three environmental water samples. Due to its potential applicability to low concentrations of Ag2S- and ZnS-NPs, this method is particularly convenient for monitoring the transformations of AgNPs and ZnO-NPs in the environment.