PLASMA PENCIL IN ANALYTICAL SPECTROCHEMISTRY – ACHIEVEMENTS AND PROSPECTS

Plasma pencil is a capacitively coupled radiofrequency (13.56 MHz) jet discharge operated in argon, helium or gas mixtures at the atmospheric pressure. It was originally designed for surface modifications of cultural heritage objects. It has been also tested in analytical spectrochemistry [1, 2] as an alternative excitation source. Due to lower excitation temperatures of about 2700- 4000 K it exhibits matrix interferences by easily ionisable elements (EIE) [3] and nowadays possible influence of anions from dissociated salts is investigated. E.g. the influence of EIE on Cu and Zn emission is apparently driven by excitation energies of Cu and Zn lines and ionization energies of EIE. However, the depression effect of sulfates on Zn emission is unexpectedly stronger than on Cu one from lowest (mg l-1) sulfate concentrations. Therefore it would be very interesting to exploit this effect for indirect determination of sulfates or sulfur in water solution. Results of this research could eventually shift the analytical capabilities of the plasma pencil towards non-metals which cannot be efficiently excited.