Spectroscopic diagnostics for evaluation of the analytical potential of argon plus helium microwave-induced plasma with solution nebulization

An Ar+ He mixed-gas microwave-induced plasma (MIP) has been investigated for use as an excitation source for optical emission spectrometry (OES) with solution nebulization. Regarding spectroscopic diagnostics via plasma temperatures and electron number density, the study compares excitation conditions in Ar, He and Ar+ He plasma. Spatial emission profiles and radial distribution of electron number density have been determined to study energy transfer in the plasmas. The addition of He to Ar produces a plasma capable of ionizing metals with ionization potential in the range of 6-10 eV more efficiently than the pure Ar plasma. The best excitation conditions for metallic elements were obtained with the Ar + 20% He plasma due to increase of rotational temperature up to 3900 K and argon excitation temperature up to 7500 K as well as MgII/Mg I line intensity ratio. The detection limits for ionic lines of some metals for the Ar+ He mixed-gas plasma are 2-7 times lower than for Ar-MIP-OES.