INFLUENCE OF THE GENERATOR FREQUENCY ON THE ANALYTICAL CHARACTERISTICS OF FAPES

A preliminary study of the influence of generator frequency on the operating and analytical characteristics of atmospheric-pressure rf He and Ar plasmas in a FAPES (Furnace Atomization Plasma Emission Spectrometry) system is presented. Apparent forward powers of 50 W were used to establish He plasmas at 13.6,27,40, and 54 MHz and Ar plasmas at 27 and 40 MHz. He and Ar excitation temperatures were of comparable magnitude (approximately 3400 K) and exhibited a monotonic increase with operating frequency. Both plasmas produced complex background structure due to excitation of molecular impurities. Significant was the presence of carbon-containing molecules (CN, C2) in the Ar plasma as a result of its enhanced sputtering capabilities. Analyte sensitivity increased with frequency, but detection limits were frequency independent. Sensitivities (peak height and area) for Ag, Cu, Mn, Pb, Ni, and Fe were consistently greater in the Ar plasma.