Preliminary Investigations of High-Frequency Atmospheric-Pressure Plasma Jet for Atomic Emission Spectrometry

Abstract

The 27.12- and 13.56-MHz plasma-jet discharges are generated in argon at atmospheric pressure. The plasma originates inside the nozzle of the bored metal power electrode and outflows against the counter-electrode. The discharge has a column shape with the diameter about 0.7-1.5 mm and the length 5-30 mm. The 27.12 MHz/100 W and 13.56 MHz/1 500 W generators are operated at a power of 100 and 200 W, respectively. Stable discharges are obtained within the range from 0.3 to 0.9 dm3 min-1 Ar. The 27.12 MHz/100 W discharge is capable of accepting dry aerosol while the wet aerosol extinguishes this plasma. On the contrary, wet aerosol can be introduced into the 13.56 MHz/200 W plasma. The vibrational temperature of 3 000 K has been determined based on the intensity of the molecular band of the N2 2nd positive system (365-383 nm) in the 27.12 MHz discharge. Intensity vs concentration dependences have been measured with Li 670.784, Na 588.995, Na 589.592, K 766.491 and Rb 780.023 nm lines. Limits of detection in the 27.12 MHz/100 W discharge coupled to an ultrasonic nebulizer with desolvation are 0.1 Li, 30 Na, 10 K and 3 ng cm-3 Rb. Limits of detection in the 13.56 MHz/200 W discharge connected to a pneumatic concentric Meinhard nebulizer is 8 ng cm-3 Li.