Characterization of analyte absorption profiles in a power-amplitude modulated inductively coupled argon plasma

Analyte absorption profiles were generated using a square wave power-amplitude modulated inductively coupled plasma (ICP). Atomic absorption was achieved by the coaxial orientation of the ICP torch along the optical axis of the spectrometer. Incident radiation, from a hollow cathode lamp, was passed through the sample introduction channel of the torch and through the central channel of the plasma. Modulation frequencies investigated were 10, 20, 30, 40, 50, 100 Hz. The magnitudes of the square wave power step were 50, 150, 250, 400, 500, 650, 850, 950 W from a steady state power level of 1500 W. Three absorbance maxima were observed between 2 and 15 ms after the decrease in the applied forward power. These maxima are suggested to be dependent on the analyte, changes in radial gas dynamics and changes in linear gas velocity. The calculated absorbance, from integrating over the 2-15 ms time period, was shown to return values comparable to those taken at the peak maxima but with improved precision and accuracy. (C) 1997 Elsevier Science B.V. All rights reserved.