Temporal analysis of ion arrival for particle quantification

Abstract

Inductively coupled plasma mass spectrometry (ICP-MS) is a powerful technique for accurately and precisely measuring particles. Built on instrumentation developed for steady state signals, traditional detection and quantification of particles with ICP-MS instruments is based on signal intensity rising above background within an integration window. This research presents results with time stamp digitization of all single ion detection events with no predetermined integration windows. With this method particles are distinguished from background by the short burst of ions (10's to 100's of μs) associated with a particle passing through the plasma. That is, particle signal is identified by the timing between successive ion arrivals at the detector. The new method allows for fast, efficient, and sensitive detection of micro and nanoparticles and provides a powerful means to discriminate against non-particle backgrounds. We tested the method with standard gold nanoparticles, uranium particles from an aerosol created during laser ablation, and iron nanoparticles. The results show efficient detection of nanoparticles separated from interfering background. The timing based method also enabled the association of a single mass 236 count with ²³⁶U uranium in a particle rather than background.