Optimization of an Infrared-Heated Sample Introduction System for Single-Particle Inductively Coupled Plasma Mass Spectrometry Analysis of Metal-Labelled Ion-Exchange Polymer Microparticles

Abstract

Single particle inductively coupled plasma mass spectrometry (spICPMS) is increasingly employed for quantification of microplastics (MPs). However, routine analysis of polymer MPs remains constrained by the poor transport efficiency (TE) of conventional pneumatic nebulization systems and by limited sensitivity for carbon-based detection. In this study, an infrared (IR)-heated modified baffled cyclonic spray chamber was used for spICPMS, and an electrostatic Ba²⁺ labeling strategy was introduced to enable sensitive, particle-by-particle characterization of functionalized polymer MPs. For 4.5-µm sulfonated polystyrene/divinylbenzene ion-exchange MPs, IR heating (135-150 °C) increased the number of detected events approximately 20-fold relative to a Scott double-pass chamber, yielding a TE of 60 ± 7%. For 10-µm MPs, 11% TE resulted under optimized conditions, extending the practical upper size range. For unlabeled MPs monitored via ¹³C⁺, the IR-heated system increased event counts by greater than 20-fold (from 170 ± 40 to 4300 ± 600 for 4.28-µm MPs; from 7.0 ± 4 to 350 ± 50 for 10-µm MPs). Ba²⁺ labeling of sulfonate sites provided accurate size estimates (4.2 ± 2.4 µm and 10.3 ± 3.6 µm) consistent with independent scanning electron microscopy measurements, demonstrating a potential characterization method using functional-group-associated heteroatom content at the single-particle level.