Characterization of a high-sensitivity ICP-TOFMS instrument for microdroplet, nanoparticle, and microplastic analyses

Abstract

We report the capabilities of an inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) instrument for single-droplet and single-particle analysis. The icpTOF-S2 (TOFWERK AG) is a high-sensitivity version of the icpTOF instrument series that features a shorter flight distance, which allows highly time resolved single-particle measurements (down to 12 μs/spectrum). The mass resolving power of the icpTOF-S2 is ∼850 at full-width half maximum and the instrument can record quasi-simultaneous full-element mass spectra—from mass-to-charge (m/z) 6 to 254. The icpTOF-S2 provides absolute sensitivities of up to 564 counts per fg and detection efficiencies of 1 ion per 6100 atoms for ¹⁷⁵Lu. These sensitivities enable single-digit attogram detection limits and theoretical particle-size detection below 10 nm in diameter for most sensitive elements, such as U, Th, and Lu. We demonstrate accurate size distribution measurement for gold nanoparticles with a mean diameter of 15 nm. With the instrument tuned for low-m/z sensitivity, we demonstrate the detection and quantification of carbon in polystyrene bead microparticles that have an average diameter of 3.1 μm. The determined critical mass for ¹²C detection is 3.2 pg and the critical diameter is 1.8 μm. Linear dynamic range for single-particle and single-droplet analysis spans 4 orders of magnitude, from 1 to 20 000 count(s) per particle event. The instrument's abundance sensitivity is around 2000 ppm, and this abundance sensitivity shows time-dependent variability as a function of intense ion spikes from microdroplets or large particles.