Ligandless Surfactant-Assisted Emulsification Microextraction and Total Reflection X-ray Fluorescence Analysis for Ionic Gold Traces Quantification in Aqueous Samples and Extracts Containing Gold Nanoparticles.

Due to the current use of gold nanoparticles (AuNPs) in many fields and their potential dissolution/transformation into ionic gold (Au3+), there is an increasing interest in methods enabling the discrimination of Au3+ from AuNPs in environmental samples. In this contribution, the combination of a novel ligandless surfactant-assisted emulsification microextraction procedure (LL-SAEME) with total reflection X-ray fluorescence spectrometry (TXRF) is proposed for the isolation and preconcentration of Au3+ in aqueous extracts containing AuNPs. The method is fast, simple, and involves low operating costs and low consumption of reagents in comparison with other spectroscopic methods. It is based on the formation of a gold hydrophobic compound with the cationic surfactant cetyltrimethylammonium bromide (CTAB) which is extracted in a few microliters of 1,2-dichloroethane. After shaking the solution by hand for 5 s, the mixture is centrifuged for 3 min at 2000 rpm and 5 μL of the organic phase containing the gold ions are deposited on a quartz reflector to carry out the TXRF analysis. Using this approach, the limit of detection for gold was 0.05 μg/L and a good linearity ( R2 > 0.99) was assessed in the range of 1-500 μg/L. Moreover, no matrix effects were observed when ionic gold was extracted from different types of water such as river, mineral, and tap waters as well as in synthetic aqueous solutions containing other ions, AuNPs, and dissolved organic matter. As a study case, the developed LL-SAEME-TXRF method was applied to monitor AuNPs stability in soils in laboratory-controlled experiments by means of Au3+ monitoring over time.