Single-particle Isotope Ratio Analysis of Lanthanides-Doped Microplastics Using Inductively Coupled Plasma Time-of-Flight Mass Spectrometry

Abstract

The large-scale production and use of engineered nanoparticles (ENPs) has led to their release into the environment, posing risks to both ecosystems and human health. The elemental and isotopic compositions of ENPs can serve as "fingerprints" for identifying their sources and tracking their fate. Single Particle-Inductively Coupled Plasma-Mass Spectrometry (SP-ICP-MS) is a promising tool for such fingerprinting. However, the commonly used quadrupole-based ICP-MS instruments have limitations in detectig multi-element and analyzing isotope ratios in single particles. In this study, we developed a novel method for analyzing isotope ratios in single particles using Inductively Coupled Plasma Time-Of-Flight Mass Spectrometry (ICP-TOF-MS). Three isotope ratios (153Eu/151Eu,142Ce/140Ce, and 176Lu/175Lu) in lanthanide-doped microplastics were determined using two commercial ICP-TOF-MS, the icpTOF 2R and CyTOF Helios. We found that the signal intensity, accuracy, and precision of isotope ratio measurements in single microplastic particles were significantly improved using the icpTOF 2R combined with collision cell technology (CCT). After adding collision gas (95.5% He and 4.5% H2) into the collision cell of the icpTOF 2R, single particle signals were significantly prolonged from 0.60±0.18 ms (standard mode) to 0.91±0.16 ms (CCT mode). We also found that isotope ratios results of the icpTOF 2R were more accurate than those from the CyTOF. The developed method will offer a valuable tool for isotope ratio analysis of single particles and show great potential in scientific applications.