Single particle inductively coupled plasma mass spectrometry: evaluation of three different pneumatic and piezo-based sample introduction systems for the characterization of silver nanoparticles

Engineered nanomaterials are used increasingly around the world. In recent years, environmental concerns have being raised that call for risk assessment, toxicity studies, and nanosafety policies. It is therefore important to provide analytical tools that are able to characterize various types of nanomaterials in a sensitive and fast fashion. In this study, the analytical performance of three sample introduction systems, a PFA micronebulizer with a Peltier-cooled cyclonic spray chamber (PC3), a PFA micronebulizer with a heated cyclonic spray chamber and three-stage Peltier-cooled desolvation system (APEX Q), and a monodisperse droplet generator (Microdrop) with an in-house built spray chamber, was compared for the characterization of silver nanoparticles (Ag NP) with different sizes (20-100 nm) using single particle inductively coupled plasma mass spectrometry (SP-ICP-MS). With continuous polydisperse and pulsed monodisperse droplet sample introduction, single 30 nm NP (PC3) and 20 nm NP (APEX Q, Microdrop), respectively, were successfully detected. Detection efficiencies (20-100 nm Ag NP) were in the range of 5.8 x 10(-5) to 8.2 x 10(-5) counts per atom, cpa (PC3), 7 x 10(-5) to 9.5 x 10(-5) cpa (APEX Q), and 8.1 x 10(-5) to 1.2 x 10(-4) cpa (Microdrop). For a given nanoparticle sample, the variation of the relative standard deviation (RSD) of the size distribution width among the three systems was found to be 1-4% (e. g. 1.3% for 100 nm Ag NP with RSDs of 16.3%, 16.8%, and 17.6% for Microdrop, APEX Q, and PC 3, respectively). Size measurements performed by SP-ICP-MS were validated by transmission electron microscopy measurements. Because silver toxicity depends on the silver species in the sample, simultaneous detection of Ag NP and free Ag(I) ions was studied with droplet sample introduction.