Exploring the performance of quadrupole, time-of-flight, and multi-collector ICP-MS for dual-isotope detection on single nanoparticles and cells.

To meet the demand for multi-element/isotope analysis at the single nanoparticle (NP) or cell level, different types of inductively coupled plasma mass spectroscopy (ICP-MS) have been used to simultaneously monitor multiple mass-to-charge ratios in single-particle/cell ICP-MS (SP/SC-ICP-MS) analysis. Systematic evaluation and comparison of the performance of these techniques are urgently required. Herein, three ICP-quadrupole (Q)-MS, two ICP-time of flight (TOF)-MS, and one multi-collector (MC)-ICP-MS instruments were employed to simultaneously detect ¹⁰⁷ Ag and ¹⁰⁹ Ag on single Ag NPs and Ag-exposed cyanobacteria cells. The evaluation was conducted by comparing the measured event-specific ¹⁰⁹ Ag: ¹⁰⁷ Ag ratios with the natural ratio. Duration of NP or cell events and time resolution in the peak hopping mode were the main factors affecting the performance of ICP-Q-MS. Under the optimal condition (100 μs for both dwell time and settling time), less than 45% of the NP or cell events had a ¹⁰⁹ Ag: ¹⁰⁷ Ag ratio deviating <30% from the natural ratio. Most events obtained via ICP-TOF-MS were paired events with both isotopes detected. For large-size NPs and cells with high exposure levels, nearly 80% of the events had a ratio deviation within ±30%. MC-ICP-MS performed particularly well in isotope determination with all the events having a ratio deviation within ±5%. For ICP-TOF-MS and MC-ICP-MS, the signal intensity of the events was the main factor affecting the accuracy of the measured ¹⁰⁹ Ag: ¹⁰⁷ Ag ratios due to the counting statistics. The established methods and results provide insight on the analyses of two elements/isotopes or more on single NPs or cells. Based on the comparison of the advantages and limitations of these instruments, this study provides a critical reference for future multi-element/isotope SP/SC-ICP-MS analyses.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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