Particle generated spectral interferences in single particle ICP-MS: a roadblock to accurate nanometrology

Abstract

The recent expansion of single particle inductively coupled plasma mass spectrometry (spICP-MS) for analysis of inorganic nanoparticles (NPs) in environmental and laboratory samples requires continued method development to ensure accurate characterization. Spectral interferences in spICP-MS analysis are often not fully addressed, especially particle generated interferences. Discrete ion clouds from ablated NPs entering the plasma form doubly charged and polyatomic species in a manner similar to dissolved ions that contribute to the continuous background signal. spICP-MS analysis of Y- and Nd-NP suspensions resulted in NP detections that are falsely identified as Pd, Ge, and As NPs due to interferences of YO⁺ and Nd²⁺. Use of a dynamic reaction cell (DRC) eliminated YO⁺ interferences, while Pd NPs were still accurately measured in mixed suspensions of Pd- and Y-NPs. A strong correlation was observed between the magnitude of interferences in solution mode and single particle mode, supporting a similar mechanism of interferent formation in the plasma for dissolved and NP-associated ions. Additionally, interference formation was affected by changes in nebulizer gas flow in a manner similar to dissolved ions. We conclude that particle generated interferences must be avoided or eliminated to ensure accurate nanometrology.