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A flexible laser excited fluorescence system has been used to trace ion trajectories in the first vacuum stage of an inductively coupled plasma mass spectrometer. The system has been used to record the spatial distributions of ions immediately upstream from the sampling cone and in the 10 mm downstream from the cone for a variety of positions of the plasma with respect to the sampling cone. The data were used in turn to test the efficacy of scanning the plasma across the sampling cone to generate maps of ion distributions in the plasma. The maps generated by scanning the plasma across the cone are close approximations of the ion distribution immediately upstream from the sampling cone, but are not representative of distributions in an unperturbed plasma.

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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 AE 40 K, and conditions typical of ''hot'' plasmas, with a measured temperature of 7380 AE 30 K. Addition of 100 mg L À1 of lithium lowered the temperature in the plasma significantly, while increasing the water load delivered to the plasma raised the temperature.