Collisional dampening for improved quantification in single particle inductively coupled plasma mass spectrometry

Abstract

Inductively coupled plasma mass spectrometry (ICP-MS) is a powerful method for detection and quantification of nanoparticles. Unfortunately, the linear dynamic range of single particle analysis is hindered by "unruly" transient signals, momentary pulse pile-ups at the electron multiplier detector. This study seeks to extend the dynamic range of ICP-MS nanoparticle quantification via addition of a collision gas in the collision cell of the ICP-MS. The collision gas temporally broadens the nanoparticle signal resulting in decreased pulse pile-up and increased integrated intensity, up to a point where scattering losses begin to dominate. We tested collisional broadening with a dual mode simultaneous secondary electron multiplier (pulse counting switching to analog) and the same detector configured for pulse counting only operation. With no collision gas and the detector operating in its standard dual mode, the data shows a linear response for gold nanoparticles from 20 nm (smallest measured size) to 150 nm. With the addition of helium as a collision gas in the cell, the linear range extends up to 250 nm. The data collected exclusively from the pulse counting mode shows that with no collision gas there is a linear response for gold nanoparticles from 20 nm to 60 nm. While the signal slightly improves with the addition of a collision gas, the linear range fails to extend up to 80 nm, the next largest nanoparticle size in this study. The addition of a collision gas used together with the dual mode detector shows a promising path forward towards mitigating unruly transient signals, improving the dynamic range of nanoparticle quantification.

Keywords: Collisional dampening; Inductively coupled plasma; Mass spectrometry; Single nanoparticle.