Single Particle Inductively Coupled Plasma Mass Spectrometry with Nanosecond Time Resolution

In this proof-of-principle study, we present our contribution to single particle inductively coupled plasma mass spectrometry (spICP­MS) developments with a novel in-house built data acquisition system with nanosecond time resolution (nsDAQ) and a matching data processing approach. The new system can continuously sample the secondary electron multiplier (SEM) detector signal and enables the detection of gold nanoparticles (AuNP) as small as 7 nm with a commercial single quadru-pole ICP­MS instrument. Recording of the SEM signal by the nsDAQ is performed with a dwell time of approximately 4 ns. A tailored method was developed to process this type of transient data, which is based on determining the temporal dis-tance between detector events that is denoted as event gap (EG). We found that the inverse logarithm of EG is proportional to the particle size and the number of detector events corresponding to a particle signal distribution can be used to calibrate and determine the particle number concentration of a nanoparticle dispersion. Due to the high data acquisition frequency, a statistically significant number of data points can be obtained in under 30 s and the main measurement time limitation for analyses is merely the sample uptake time and rinsing step between analyte solutions.