Spatially resolved radial excitation temperatures and radial electron density distributions experienced by analyte species in the observation zone of 15 to 25 mm above the load coil of a toroidally shaped, inductively coupled argon plasma are presented and related to the analytical performance of these plasmas. A comparison of radial temperatures measured with support gas (Ar I) lines and with a typical analyte thermometric species (Pe I) at 15 mm above the load coil is given. Radial (Fe I) excitation temperatures obtained at three observation heights are compared for aerosol carrier flows of 1.0 and 1.3 liters/min. The addition of a large amount of an easily ionized element (6900 µg of Na per ml) did not significantly change Fe I excitation temperature distributions at the respective aerosol carrier flows and observation heights. A comparison of radial electron density distributions measured with Saha-Eggert ionization and with Stark broadening methods is given for an observation height of 15 mm above the load coil. The differences between electron density values obtained by these methods is discussed. The effect of addition of 6900 µg of Na per ml on Saha-Eggert electron density distributions at three observation heights is also discussed.
Electron density measurement of inductively coupled plasmas by terahertz time-domain spectroscopy (THz-TDS)