Determination of zinc in individual airborne particles by inductively coupled plasma mass spectrometry with digital signal processing

Abstract

A high-speed digital signal processing system has been developed as an individual particle analyzer combined with ICP-MS to achieve signal profiling with a time resolution of 20 µs and a lower detection limit. When air samples are directly introduced into the plasma, the ICP-MS generates a train of pulses corresponding to the ion population of a given element in the plasma. The present system can digitally count pulses from a channel electron multiplier used as a detector in ICP-MS in a duration time of 20 µs each. A time-resolved signal profile stored in the computer memory shows that each flash signal derived from individual airborne particles has a sharp peak with a time-width of 0.1–0.5 ms. The detection limit for zinc in a particle is lowered to sub-fg levels by precisely measuring the signal strength for each particle under a condition of low background noise. The profile of the flash signal for individual particles reflects the evaporation and ionization processes of each particle in the plasma and the extraction process of ions through the sampling orifice of the mass spectrometer.