A pulsed atmospheric-pressure discharge generated in contact with flowing electrolyte solutions for metal element analysis by optical emission spectrometry

A novel atmospheric-pressure plasma source has been developed for the detection of metal ions in aqueous solution by optical emission spectrometry. In contrast to the common solution cathode glow discharge, this source is sustained by using an alternating-current power supply coupled with a high voltage diode. The electrical characteristics and spectral characteristics of this plasma source are discussed. The effects of operating parameters, including the acid anion, electrolyte pH, discharge voltage, discharge frequency, inter-electrode distance, sample flow rate and vertical distributions of spectral signals, are investigated. The spectral intensities and standard deviations (SDs) of background signals of this source are much lower than those of other electrolyte-electrode devices. In addition, metal element emissions have the same optimum spectral emission positions in the plasma. The detection limits of Li, Na, K, Rb, Cs, Sr and Mg are determined to be 0.0054, 0.0011, 0.0029, 0.04, 0.054, 2.5 and 0.26 mg L-1, respectively. The proposed excitation source provides a promising technique for the detection of metal ions in aqueous solution samples.