Towards the harmonization of raw data processing in single particle inductively coupled plasma mass spectrometry

Despite the availability of advanced data processing tools for single particle inductively coupled plasma mass spectrometry (SP-ICP-MS), users cannot fully trust on them to obtain reliable and accurate information due to their lack of validation. Along this work, current approaches for data processing have been evaluated in depth, paying special attention to the criteria and expressions used for calculation of critical values concerning the discrimination of baseline and particle readings, the counting of particle events and the determination of their total intensities, in order to promote their harmonization within the field, although focusing on quadrupole instruments. Baseline intensity was the most critical variable, since its magnitude determines which approach, Poisson or Gaussian, must be applied for discrimination of baseline and particle readings depending on its magnitude. Application of the corresponding approaches with a coverage factor of 5 led to the occurrence of less than 10 false positives (baseline readings considered as particle events) in a variety of experimental conditions (baseline intensities, number of readings, dwell times). The use of less demanding coverage factors (e.g., 3) led to increased false positives, particularly in the presence of nano- and microparticles and working at short dwell times, due to the higher occurrence of low-intensity particle events. Therefore, such conditions should be avoided. Processing data from nano and microparticle suspensions measured at different dwell times and baseline levels with the free-access and open-source tool SPCal, resulted in reliable counting numbers and total intensities when the adequate critical values were applied. Consequently, this tool allowed the validation of a proprietary software as a proof of concept, confirming comparable results, except for the counting of particle events with high baseline levels or when using short dwell times, as long as the proposed approaches for the calculation of critical values, which were not originally implemented in such proprietary software, were applied.