Calibration of single-particle inductively coupled plasma-mass spectrometry (SP-ICP-MS)

Abstract

We have identified incomplete particle vaporization and non-linear detector response as the major factors that cause the non-linearity of SP-ICP-MS measurements at high particle mass. The contribution of incomplete vaporization to the deviation from the linearity of the ICP-MS intensity is estimated using a mathematical model of particle vaporization. The non-linear detector response in the pulse-counting mode is due to the overlapping of the analyte ions at the detector within the 40 ns dead time of the electron multiplier. The overlap can be severe because of the relatively short pulse duration of 300 μs of the ion plumes of the discrete sample particles. The non-linear detector response has been modeled using Poisson statistics. We have also examined the applicability of calibration methods based on the standard particles, discrete standard solution droplets, and continuous nebulization of standard solution. The standard-solution calibration method requires linear calibration curves. The method may also suffer from errors due to the difference in the sensitivity of the standard solution and sample particles. Calibration using standard particles and discrete standard solution droplets do not have these limitations.