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.