An impact of the material and diameter of tubes in the flowing liquid cathode atmospheric pressure glow discharge system on its analytical performance - Preliminary study

Tubes of different diameters and materials were tested as solution (tungsten, molybdenum, titanium, corundum, quartz, and graphite) and gas (tungsten, molybdenum, and titanium) delivery tubes for the flowing liquid cathode atmospheric pressure glow discharge (FLC-APGD) microplasma system. For work purposes, FLC solu-tions both with and without the addition of formic acid were tested and the results were compared. Additionally, to elucidate the impact of various combinations of tubes on the excitation conditions in the discharge, the excitation (Texc(H)), rotational (Trot(OH)), and vibrational (Tvib(OH)) temperatures, as well as the electron number density were all determined. It was found that certain combinations of the tubes affected the discharge stability, therefore, either the precision was poor or the discharge could not be maintained at all. As a result, detection limits (DLs) of the studied elements were assessed for some combinations of tubes in order to establish the impact of the discharge stability on the background fluctuations. It was noticed that certain materials of the tubes, namely tungsten and corundum, were superior in terms of their resistance to the conditions under which the discharge was sustained. The analytes signals were found to be slightly affected by changing tubes, however, it was shown that the tungsten and corundum tubes provided better results in terms of signals intensity, than the other ones. Additionally, the commonly used combination of glass and graphite tubes turned out to give the lowest analytes signals and relatively high DLs.