Solid-phase extraction of Hg(II) using cellulose filters modified with silver nanoparticles followed by pyrolysis and detection by a direct mercury analyzer

In this work, a new approach for ultrasensitive detection of Hg(II) in waters following preconcentration by filtration through paper modified with nanoparticles (NPs) is described. Reduction of Hg(II) to Hg(0) without chemical reagents followed by amalgamation of Hg-0 was performed using cellulose substrates containing AgNPs synthetized in situ. Enriched filters were introduced in a direct mercury analyzer for Hg determination by atomic absorption. Different synthesis procedures and types of NPs (AgNPs, AuNPs and PdNPs), filtration systems and characteristics of filter papers were fully investigated. In addition, other relevant variables influencing the solid-phase extraction of Hg such as sample volume and pH were studied. Cellulose substrates modified with AgNPs were characterized by scanning electron microscopy, imaging in backscattered electron mode and coupled with energy-dispersive X-ray spectrometry. Colorimetry measurements on filter surface were also carried out. Homogeneous distributions of AgNPs with a size of 30-50 nm on filters and high stability of the coatings under different storing conditions were obtained. A preconcentration factor around 3500 and a limit of detection of 0.2 ng/L Hg were achieved for a 100 mL sample volume. The repeatability and reproducibility expressed as relative standard deviation were 5 and 9%, respectively. The presence of other species in natural waters including methylmercury did not cause any effect, thus showing a high selectivity of the method for Hg(II) sorption. Certified reference materials and synthetic waters (seawater, dialysis water, wastewater and mineral water) were analyzed. Recoveries in the range of 92-105% were observed in all cases.