Effect of Operating Frequency on Spatial Features of the Inductively Coupled Plasma

Abstract

An unambiguous comparison has been made of the spatial features of a 27.12 and a 40.68 MHz inductively coupled plasma. Experiments were carried out with a switchable-frequency, solid-state radio-frequency generator from the Leco 2000 system. Several features of analytical significance have been evaluated in a spatially resolved fashion. Results from optimization of the magnesium ion-to-atom (Mg II/Mg I) line-intensity ratio have been compared. The volume of the two discharges was estimated from molecular nitrogen-ion emission, and a spatially resolved map of the Fe(I) excitation temperature was determined by means of a Boltzmann analysis at each spatial location. Calcium and magnesium ion-to-atom line-intensity ratios have been calculated throughout both plasmas. Finally, limits of detection are presented. The results indicate that the plasma operated at 40.68 MHz provides slightly better figures of merit, although fundamental parameters suggest a lower degree of analyte excitation. This difference is explained by examining the results of a simulation of plasmas operated at 27.12 and 40.68 MHz.