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 mu m and 2-5 mu m). 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.