Source gas kinetic temperatures in an ICP-MS determined by measurements of the gas velocities in the first vacuum stage

Abstract

Gas kinetic temperatures in the inductively coupled plasma ion source of a plasma-source mass spectrometer were determined for a range of instrument conditions by diode laser spectroscopy. Centerline velocities of argon atoms in the supersonic expansion in the mass spectrometer’s first vacuum stage were calculated from Doppler shifts in the excitation spectra of the probe atoms. Source stagnation temperatures were in turn calculated from the atom velocities. Among the conditions studied were a set typical of “cold” plasmas, with a measured temperature of 5080 ± 40 K, and conditions typical of “hot” plasmas, with a measured temperature of 7380 ± 30 K. Addition of 100 mg L⁻¹ of lithium lowered the temperature in the plasma significantly, while increasing the water load delivered to the plasma raised the temperature.