Background and Theory

Single-particle ICP-MS is a technique to analyse particulate matter in aqueous samples. It is essentially the same as any time-resolved ICP-MS measurement, but with a significantly shorter acquisition or event time. The rapid collection of data (typically sub millisecond) allows the resolution of individual particles as they are nebulised, atomised and extracted in discrete ion clouds. For a comprehensive review of spICP-MS as a nano-particle analysis technique see Laborda, Bolea and Jiménez-Lamana [1].

Thresholds

One of the major difficulties with spICP-MS is establishing theoretically sound detection thresholds. These pages discuss the use and implementation of Gaussian, Poisson and Compound-Poisson thresholds in SPCal.

• Thresholds for spICP-MS
  • Poisson
  • spICP-ToF: Compound-Poisson
    • Log-normal approximation
    • Lookup Table
  • Threshold selection
  • Error rates

Parameter Recovery

The methods used in SPCal for thresholding ICP-TOF data require knowledge of the underlying distribution. Here we explain how we can recover this knowledge from existing data and use it to accurately threhold.

• Recovery of compound-Poisson-lognormal parameters
  • Method for recovery
  • Automatic calculation of SIA shape in SPCal

Publications

A previous, quadruple only, version of SPCal was published and is available here:

• Lockwood, T. E.; Gonzalez de Vega, R.; Clases, D. An Interactive Python-Based Data Processing Platform for Single Particle and Single Cell ICP-MS. Journal of Analytical Atomic Spectrometry 2021, 36 (11), 2536–2544. https://doi.org/10.1039/D1JA00297J.

Several other publications discussing aspects of the new ToF version are also available:

• Gonzalez De Vega, R.; Lockwood, T. E.; Paton, L.; Schlatt, L.; Clases, D. Non-Target Analysis and Characterisation of Nanoparticles in Spirits via Single Particle ICP-TOF-MS. Journal of Analytical Atomic Spectrometry 2023, 10.1039.D3JA00253E. https://doi.org/10.1039/D3JA00253E.

• Lockwood, T. E.; Gonzalez De Vega, R.; Du, Z.; Schlatt, L.; Xu, X.; Clases, D. Strategies to Enhance Figures of Merit in ICP-ToF-MS. Journal of Analytical Atomic Spectrometry 2024, 39 (1), 227–234. https://doi.org/10.1039/D3JA00288H.

• Lockwood, T. E.; Gonzalez de Vega, R.; Schaltt, L.; Clases, D. Accurate thresholding using a compound-Poisson-lognormal lookup table and parameters recovered from standard single particle ICP-TOFMS data. J. Anal. At. Spectrom. 2025, 40, 2633-2640. https://doi.org/10.1039/D5JA00230C.

[1]

Laborda, F.; Bolea, E.; Jiménez-Lamana, J. Single Particle Inductively Coupled Plasma Mass Spectrometry: A Powerful Tool for Nanoanalysis. Anal. Chem. 2014, 86 (5), 2270–2278. https://doi.org/10.1021/ac402980q.