A novel atmospheric-pressure plasma source has been developed to determine metal ions in an aqueous solution by means of optical emission spectroscopy. In contrast to the conventional solution cathode glow discharge, this plasma source is sustained by a milli-second pulsed power supply. The electrical characteristics and spectral characteristics of the proposed plasma source are discussed. The effects of operating parameters, including pulse excitation and maintenance discharge voltage, pulse width, pulse modulation duty ratio, solution flow rate, and detector delay time, are investigated. Na, K, and Ca were observed to have a cumulative spectral emission time of 250 μs. Delayed acquisition times (in the case of maximum spectral intensity) are 500, 800, 800, 900, and 900 μs, respectively for Cu, Co, Cd, Mn, and Ag. The detection limits of trace elements such as Na, K, Cu, Co, Cd, Mn, and Ag were 0.080, 0.050, 3.4, 64, 69, 9.1, and 2.0 μg L⁻¹, respectively. Compared to DC-excited solution cathode glow discharge, the detection performance of the above elements is observed to be increased by 2.9, 1.5, 18, 5.5, 25, 1.6, and 2.1 times, respectively. The proposed excitation source provides a promising method for detecting metal ions in aqueous solution samples.