Study of a direct current atmospheric pressure glow discharge in helium with wet aerosol sample introduction systems

In this study a He DC atmospheric pressure glow discharge (APGD) is characterized under dry conditions and with the introduction of wet aerosols. The aerosols are generated by a conventional pneumatic nebulization system using a Micro Mist nebulizer placed in a double pass spray chamber according to Scott or alternatively by a custom-built drop-on-demand (DOD) system based on printer cartridges. The experiments are performed at a He gas flow of 500 mL min(-1) and 40 mA current. The influences of the H2O load on the discharge rotational temperature (T-rot), excitation temperature (T-exc) and the electron number density (n(e)) are determined. Temperature reductions when comparing dry and wet conditions are found to be around 500 K for the T-rot and 240-400 K for the T-exc. Detection limits for the elements Cd, Cu, Mg, Mn and Na are presented for pneumatic nebulization coupled to a continuous flow injection system. They are found to be between 10 mu g L-1 for Na and 140 mu g L-1 for Cu. In the case of the drop-on-demand system a value of 16 mu g L-1 for Na was obtained. The applicability of the discharge to the determination of Na in a tap water sample at concentration levels of 20 mg L-1 is shown for both introduction systems and the accuracy of the results is found to be within 1.3 mg L-1 as compared to the result of inductively coupled plasma optical emission spectrometry (ICP-OES).