Ultra-trace determination of silver nanoparticles in water samples using cloud point extraction and ETAAS

The continuing boom of nanotechnology leads to the question of the environmental fate of engineered nanoparticles. In this study an improved method for the quantification of silver nanoparticles (Ag-NPs) in environmental samples in the nanogram per litre range by means of cloud point extraction (CPE) and electrothermal atomic absorption spectrometry (ETAAS) is presented. Separation of nanoparticles from ionic silver species is achieved by addition of the ligand EDTA. A limit of detection (LoD) as low as 0.7 ng L-1 was obtained by optimizing the extraction conditions, the enrichment factor, and the ETAAS measurement conditions. In comparison to previously published studies the LoD for silver nanoparticles after CPE is improved by a factor of 10 because ETAAS detection requires no additional sample digestion after extraction. Samples of different complexity such as river water, treated and untreated municipal wastewater and synthetic solutions containing dissolved and particulate organic matter with a total organic carbon (TOC) content up to 10 mg L-1 were spiked with different concentrations of Ag-NPs and a high recovery (>80%) was found in all cases. Due to the low LoD and high tolerance levels for other particulate matter, TOC and ionic species, selective determination of Ag-NPs in municipal wastewater and also in the effluent of sewage treatment plants is now possible.