ATOMIC-EMISSION SPECTROMETRY EMPLOYING A PULSED RADIO-FREQUENCY-POWERED GLOW-DISCHARGE

A radio-frequency (rf)-powered glow discharge pulsed at 50 Hz with a 25% duty cycle is used as an atomization/excitation source for analytical atomic emission spectrometry. Compromise working conditions are established at 0.8 Torr argon pressure and 80 to 90 W peak applied power. Analyte emission intensities are found to increase with increases in discharge pressure and peak applied rf power to an upper limit corresponding with the onset of discharge instability. The observed emission signal intensity is influenced strongly by changes in the cathode-to-anode separation distance. Long-term analytical signal stability is exhibited by this source at rf powers up to 90 W in the absence of external cooling because of operation in the pulsed mode. The maximum attainable stable emission signal with pulsed operation is approximately four times greater than that attainable with steady-state operation. The analytical utility of this source is demonstrated through determinations of trace elements in coal fly ash and graphite samples with limits of detection in the tens of parts-per-million range.