RF plasma nozzle for analytical chemistry

Different plasma sources were used for chemical analysis – inductively coupled plasma, glow discharges, capacitively coupled plasma and microwave sources. Discharges at atmospheric pressure were used in most cases. Our study was aimed to rf plasma nozzle (plasma pencil) at atmospheric pressure as an alternative excitation source for analytical chemistry. Plasma pencil had been a capacitively coupled plasma rf jet discharge, operated typically in argon at atmospheric pressure. The experimental arrangement is shown in Fig. 1. The plasma was boosted by a Cesar 136 rf generator at 13.56 MHz frequency, and the correct feedback was driven by a laboratory-made matching unit keeping the reflected power close to zero. It was enclosed in a 250 mm long quartz tube (o.d. 4 mm, i.d. 2 mm). The position 6.5 cm corresponds to the ground electrode, 0 cm is the position of the sample inlet, and the power electrode is on position -1.5 cm. The main argon stream was dosed with a mass flow controller. The aerosol sample introduction system employed a peristaltic pump, and a double pass Scott spray chamber with a pneumatic concentric nebulizer. The created aerosol was transported by the carrier gas perpendicularly into the main discharge argon stream. The analytical profit of this plasma source had been shown during the determination of Li, Na, Mg, Ca, Cu and Zn in aqueous solutions as representatives of alkali, alkali-earth and transition metals [1-3]. The parameters of the plasma nozzle (rotational and excitation temperature) were calculated by optical emission spectroscopy (OES) [4]. The advantage of the tested plasma source had been lower operational costs compared with conventional inductively coupled plasma or microwave plasma excitation sources for chemical analysis.