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

ABSTRACT

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 107Ag and 109Ag on single Ag NPs and Ag-exposed cyanobacteria cells. The evaluation was conducted by comparing the measured event-specific 109Ag107Ag 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 109Ag107Ag 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 109Ag107Ag 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.