The paper estimates the nitrate ion content in foods of plant origin sold in retail stores of Podolsk, Moscow region, using 60 samples of fruits and vegetables as an example. The content of nitrate ion is assessed by a standard ionometric procedure using a MIKON-2 kit. The measurements are performed using an electrode system consisting of a nitrate selective electrode and an auxiliary silver chloride electrode with a thickened electrolyte. The measured concentrations are within acceptable limits, with the average nitrate ion content for vegetables and fruits being 47 mg/kg and 19 mg/kg, respectively. A low correlation coefficient (R2 = 0.005) between the electrical conductivity and the nitrate ion content for the studied samples is established, showing that the determination of nitrates in plant products using conductometric nitrate testers leads to false data. It is found that at Eh and pH values characteristic of the studied samples, the most stable form of nitrogen is molecular nitrogen, which thermodynamically leads to a low probability of the accumulation of significant concentrations of nitrates in the studied samples.