Silver nanoparticle-assisted preconcentration of selenium and mercury on quartz reflectors for total reflection X-ray fluorescence analysis

In this work, a new analytical approach based on the trapping of Se and Hg vapours using silver nanoparticles (Ag NPs) immobilized on quartz reflectors, prior to their determination by total reflection X-ray fluorescence (TXRF), is proposed. Ag NPs were synthesized by reduction of the metal precursor with a reducing agent in aqueous solution. Silanization with 3-mercaptopropyltrimethoxysilane (MPTMS) was used in order to modify the quartz reflectors and immobilize Ag NPs by interaction between the organosilane compound and Ag NPs. A comprehensive characterization of synthesized Ag NPs was carried out by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). SeH2 and Hg(0) vapours were generated by means of a continuous flow vapour generation system and trapped onto the quartz reflector containing immobilized Ag NPs. Different parameters involved in both the Ag NP synthesis and the continuous flow system for vapour generation and preconcentration were optimized in order to obtain the best results. Detection limits were 0.18 and 0.55 μg L−1 for selenium and mercury, respectively. Enrichment factors of 265 and 175 were obtained for Se and Hg, respectively. The new method was successfully validated against three biological certified reference materials and applied to several seafood samples. Recoveries carried out on three certified reference materials were in the range 94–106% with a relative standard deviation of 5% (N = 5).