Size detection limits in single particle inductively coupled plasma mass spectrometry: Reconsidering the selection of dwell times

Performance of single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) methods is constrained by the characteristics of the instrumentation. The commercial availability of fast data acquisition quadrupole instruments, which allow the use of dwell times in the microsecond range rather than being restricted to milliseconds, was expected to improve the performance of the technique. When data acquisition frequency is increased, individual particles are recorded as transient signals consisting of multiple-reading events instead of one-reading pulses. Since particle events must be detected above the baseline noise, the highest intensity reading of a transient signal becomes a relevant parameter whose value decreases with decreasing dwell time, as the total intensity of a particle event is independent of the number of readings per event and thus of the selected dwell time. In this work, the effect of dwell time on the attainable size detection limits has been reconsidered, achieving minimum size detection limits when dwell times in the range of 200 – 500 μs were used, regardless of the baseline level. At such dwell times, particle events from small nanoparticles (e.g., 2 – 3 times the size detection limit) were recorded within 1 – 2 readings despite the duration of particle events, which was modified working in both standard and gas reaction modes. Under these conditions, free and proprietary software capable of handling multiple-reading events allowed to process successfully the SP-ICP-MS data independently of the dwell time applied. • The lowest size detection limits in SP-ICP-MS are achieved at 200–500 μs dwell times. • At such dwell times, particle events are recorded within 1–3 readings. • Particles events can be successfully processed by using peak-based software. • The magnitude of the baseline does not affect to this behaviour.