A dc atmospheric pressure glow discharge (APGD) operated in open air atmosphere was applied as a miniaturized excitation source in analytical optical emission spectrometry. The discharge was generated in contact with a small size liquid cathode of a novel design and stably operated at a low current (20 mA) and solution uptake rate (0.6 mL min−1). The volume of the discharge was estimated to be 6 mm3, while the power density was 5 kW cm−3. For the selected elements, i.e., Ca, Cd, Cu, K, Li, Mg, Mn, Na, Rb and Zn, the detection limits, the dynamic linearity ranges and the precisions were determined to ascertain the analytical performance of this miniaturized excitation source. The concentrations of some elements (Ca, K, Mg, Mn, Na and Zn) were determined in the samples of tea and its infusions and mineral water. These results were compared to those obtained by flame atomic absorption spectrometry (FAAS) and flame atomic emission spectrometry (FAES) and a good agreement between the results was established. Additionally, the effect of the easily ionizable elements (EIEs) on the relative intensities and the signal to background ratios (SBRs) of the measured emission lines as well as the Mg II/Mg I ratio and electron number density were investigated.