Flow injection with on-line dilution and single particle inductively coupled plasma – mass spectrometry for monitoring silver nanoparticles in seawater and in marine microorganisms†
Single particle inductively coupled plasma mass spectrometry (spICP-MS) is a unique tool for detecting silver nanoparticles in environmental samples at concentrations similar to those predicted in surface waters. In this study, we present a novel flow injection spICP-MS method configured to allow for rapid on-line dilution at the tip of a pneumatic nebulizer. Such a sample introduction system permits the detection and characterization of silver nanoparticles in seawater at low ng Ag per L concentrations. Dilution (up to 1/80) accounts for the minimization of seawater originating spectroscopic interferences for both silver isotopes, whereas signal suppression caused by the matrix is corrected by utilizing a freshly prepared seawater solution containing well characterized silver nanoparticles (matrix matching) in order to determine ionization and transport efficiencies. Furthermore, we present a novel, yet straightforward method for determining silver nanoparticles and dissolved silver in marine microorganisms and/or interacting with natural organic matter. This method is based on the ultrasonication of filters used for sieving 15 L of seawater, once they are immersed in deionized water. The purpose of this approach is to lyse microorganism cell membranes and thus liberate their silver content. Subsequent flow injection spICP-MS allows for the determination of the silver nanoparticles and dissolved silver bio-accumulated in marine biota and/or interacting with natural organic matter for two different filter size fractions (i.e. 0.2–2 μm and 2–5 μm). Application of these methodologies for studying seawater microcosm and mesocosm systems allowed for the detailed monitoring of the fate of silver nanoparticles in the marine environment.