Atmospheric pressure plasmas are widely used for nitrogen fixation processes to produce ammonia NH3 or nitrogen oxides NOx , including for example nitrite NO2– or nitrate NO3–. Small scale atmospheric pressure plasma jets (APPJs) can provide the production of these species on demand at the site of consumption. The species of interest are generated by the plasma and can be dissolved in liquids, for example, in order to use them. In this work, liquid treatments were performed by an APPJ operated in a He-H2O-N2-O2 gas composition in order to investigate the influence of the gas composition on the production of hydrogen peroxide H2O2, NH3 and NO2–. A validation of two H2O2 diagnostics showed that the spectrophotometric approach using ammonium metavanadate was interfered by other species when N2 was added to the system. Thus, electrochemical sensing of H2O2 was performed. The concentrations of NH3 and NO2– were measured by commercially available test kits based on the o-phythalaldehyde-method and the Griess reagent, respectively. At low N2 admixtures, the dominant species was H2O2 with a maximum concentration of 0.9mM, while NO2– became dominant at N2 admixtures of 0.5% and higher withconcentrations of up to 1.5mM. NH3 was also present in the system and could be measured at low concentrations of less than 0.2mM in the liquid. By varying the treatment distance and the gas flow rate, insights into the transport phenomena of the species and their dissolution into the liquid could be gained. Low frequency pulsing of the RF jet led to an accumulating effect on H2O2, a reduced production of NO2– and a switch from NOx dominated production to H2O2 dominated production.