A MICROWAVE PLASMA TORCH ASSEMBLY FOR ATOMIC EMISSION-SPECTROMETRY

A new excitation source for atomic emission spectrometry, the microwave plasma torch (MPT) discharge, was developed and its analytical performance examined. The MPT works in a way that is significantly different from the ways in which the Beenakker cavity, surfatron or traditional capacitively coupled microwave plasma do. With the MPT, an argon discharge can be sustained at atmospheric pressure and at very low flow rate (10 ml/min) and low forward power (40-500 W). Under slightly different conditions, a He or N2 microwave plasma (MP) can also be sustained. The plasma from the MPT is flame-like and has a central channel. Moreover, the sample aerosol can be introduced into the plasma with or without desolvation. Since the analyte is forced to pass through the central channel of the microwave discharge, it is efficiently vaporized, atomized, excited and ionized, and causes minimal perturbation to the plasma. The parameters that effect the plasma behavior have been studied in some detail. Background emission and the emission profiles of selected analytical lines were studied. The detection limits for most elements which have been studied are in the range of 1-50 ng/ml, when an ultrasonic nebulizer with a simple desolvation system is employed. With the He MP, nonmetals including halogens are detectable even when samples are introduced in an aerosol form.