In this study, ammonia (NH3) vapor was added to an atmospheric pressure argon plasma jet generated by a sinusoidal power supply (with an applied voltage of 4 kV and frequency of 35 kHz) and it was analyzed by electrical, optical, and chemical probe measurements. A total gas flow rate of 1200 sccm under 2% flow rate of either water or ammonia solution at concentrations up to 0.75% mixed with 98% argon feeding gas. The dissipated power of the plasma jet estimated by voltage-charge plots was found to decrease continuously with increase in ammonia concentrations at a fixed applied voltage. The optical emission spectra inside the quartz tube obtained for the NH3 mixed plasma indicated the presence of nitrogen emission lines which were absent in the water only mixed argon plasma. Colorimetric measurements of hydrogen peroxide (H2O2) and nitrite () in plasma activated water (PAW) were performed at different consumed energy varied by plasma exposure time. The H2O2 concentration decreased to 4 ppm from 14 ppm, while the concentration simultaneously increased to 6 ppm from 1 ppm as the ammonia concentrations increased to 0.75% from 0% throughout 2.07  ×  103 joule energy consumption. We also analyzed the corresponding variation of pH values, in absence of ammonia, PAW leads to acidification but addition of small amount of ammonia in plasma is sufficient to make it alkaline. Additionally, we measured the hydroxyl (OH) radical density in gas and liquid phases by utilizing UV absorption spectroscopy and chemical probe method, respectively. OH radical density in both phases also decreased with the increase in the NH3 concentrations. Experimental results obtained from this experiment can be attributed to control H2O2 concentrations in the PAW via plasma-assisted nitrification.