Single particle inductively coupled plasma mass spectrometry: investigating nonlinear response observed in pulse counting mode and extending the linear dynamic range by compensating for dead time related count losses on a microsecond timescale

In single particle inductively coupled plasma mass spectrometry (spICP-MS) the detection of small nanoparticles (NP) usually requires utilization of the pulse counting signal, which entails the risk of nonlinear response for larger NP. In this work, the suitability of a traditional dead time correction (DTC) method applied to both millisecond (msTR) and microsecond (mu sTR) time-resolved spICP-MS is evaluated. A custom data acquisition system was used to record the pulse counting signal at a sustained rate of 2 x 10(5) samples per second. Model transients from microdroplets containing different concentrations of a thallium element standard and generated via a custom droplet introduction system were studied (Part A). Findings were compared to the analysis of eleven gold NP suspensions covering a size range of 10-100 nm, introduced via regular solution nebulization (Part B). Applying DTC to mu sTR spICP-MS data allowed to increase the maximum number of counts tolerated per particle or droplet four- to fifteen-fold, resulting in a linear dynamic range (LDR) of 10-60 instead of 10-40 nm AuNP, or 9-4500 instead of 9-300 mu g L-1 Tl. For Part B a cross-calibration between standard and attenuated sensitivity mode could be established, further extending the LDR (10-100 nm AuNP). Findings support the theory of dead time related count losses being the main reason for nonlinear response in pulse counting spICP-MS. However, results also indicate that DTC can lead to slightly distorted particle size distributions.