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

Abstract

Sampling of the pulse-counting signal with μs time-resolution provided a functional compensation for dead-time related count losses in spICP-MS, ultimately improving the linear dynamic range by one order of magnitude towards higher count rates.

Single Particle Inductively Coupled Plasma Mass Spectrometry with Nanosecond Time Resolution

“…The detector dead time, however, is assumed to be in the order of 50 ns. 32 Consequently, pulses (i.e. ion events) that occur within the dead time of the SEM cannot be acquired with the system.…”

“…In addition, a dead time correction approach that was already successfully used with the µsDAQ was not yet incorporated into the nsDAQ. 32 One basic consideration of spICP-MS is that the sum of counts of an individual ion cloud is directly proportional to the original particle's number of atoms and consequently proportional to the particle's mass. Under the assumption that a solid particle is perfectly spherical, the cubic root of the sum of counts is proportional to the particle size and particle size distributions can be created, accordingly.…”

“…The already known issue of data loss due to detector dead time most probably even further reduces the ratio of detected events to arriving ions. 32 Both effects have a stronger impact on ion clouds with longer duration, which causes the non-linear response. Additionally, the particle signal and background signal overlap in the log(EG) histogram, which leads to inaccurate determination of a definite range of the particle signal, especially for smaller particles.…”

Number of spikes in single particle ICP-MS time scans: from the very dilute to the highly concentrated range

“…2 is reminiscent of mathematically analogous problems involving detector dead times, which are well documented for photon or ion counting and for the detection of nuclear events since the 1930s [17][18][19][20] . Such questions have been recently studied in the sp-ICP-MS context 21 . There is a mathematical one-to-one correspondence -but not a physical one -between the pile-up problem we considered and dead time problems.…”

“…We stress that we did not consider the dead time τ dead of the detector in this work. Indeed, for electron multipliers, τ dead is typically worth a few dozens of nanoseconds [21][22][23] , which is much less than τ p . We thus neglected τ dead in our analysis.…”