Kinetic Energy Distributions of Positive Ions in an Inductively Coupled Plasma Mass Spectrometer

A simple method is described for the approximate measurement of the ion energy distribution in an inductively coupled plasma-mass spectrometer (ICP-MS) with a continuum flow sampling interface. The average ion kinetic energy, kinetic energy spread, and maximum kinetic energy are evaluated from a plot of ion signal as a function of retarding voltage applied to the quadrupole mass analyzer. The effects of plasma operating parameters on ion signals and energies are described. In particular, kinetic energy is a sensitive function of aerosol gas flow rate. This behavior is attributed to a nonthermal, possibly electrical, interaction between the plasma and the sampling interface, which is induced by the presence of the axial channel in the ICP.