Nanomaterials are increasingly used in industrial processes, manufactured goods, medicines, and consumer products such as cosmetics, sunscreen, and food. The measurement of nanoparticles (NPs) is the focus of attention because the fate of NPs in the environment and the potential for toxic effects once absorbed into the body are not yet well understood.
ICP-MS is a well-established technique for measuring the elemental content of materials; the relatively recent development of Single Particle acquisition mode (spICP-MS) now provides a powerful method to characterize the NP content of a sample. spICP-MS is used to record the target element signals generated from individual NPs in the solution analyzed, allowing simultaneous determination of the number, concentration, and size of particles present, as well as the dissolved element concentration. This approach has been developed by many researchers [1-4], and modern ICP-MS instruments can now offer automated acquisition and calibration approaches to support NP characterization. Current ICP-MS systems use short dwell times and acquire data continuously for a single isotope with no settling time between measurements. This enables the detection of smaller particles because, while the total background counts over the dwell period are reduced proportionally, the signal from the particle plume is not reduced. However, if the dwell time is shorter than the duration of the plume, which is typically around 0.5 ms, then the analyte signal is also reduced with decreasing dwell time. This increases the error in the counting statistics. It is important to maintain statistically valid count rates by using the highest possible sensitivity (signal-to-noise) and an appropriate dwell time.
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