Possibilities and analytical properties of the radiofrequency plasma pencil operating in the continuous and in the pulsed mode

Abstract

A two-electrode capacitively coupled plasma jet discharge operating at a 13.56 MHz symmetrical sinusoidal frequency carrier wave in a continuous mode and in a pulsed mode is described in this paper. The Internally pulsed mode was realised by the frequency modulation using a symmetrical rectangular frequency of 22 kHz with a duty cycle of 90%. The pulsed mode has an effect on the electron number densities ranging from 1 × 10¹⁴ to 1.2 × 10¹⁵ in the pulsed mode and from 1.7 × 10¹⁴ to 1.0 × 10¹⁵ cm⁻³ in the continuous mode, gas temperatures 670–950 K in the pulsed and 630–880 K in the continuous mode, excitation temperatures 3100–4250 K in the pulsed and 3500–4280 K in the continuous mode, slopes and intercepts of the calibration lines and limits of detection and a weak effect on the coefficients of determination. All these parameters were measured at three different positions from the sample inlet of the plasma pencil. Most line intensities and the excitation temperature decreased while calcium lines and gas temperature calculated from OH radicals increased in the pulsed mode. These results indicate a strong interaction between calcium species and OH radicals. Analysis of real low mineralized water samples showed similarity of the yielded results to those obtained by reference ICP-OES.