A method for automatically determining the concentration of nitrite in a liquid sample includes: determination of the extinction of the liquid sample at a wavelength λ of 150-250 nm, addition of a nitrite reducing agent to the liquid sample, determination of the extinction of the reduced liquid sample at a wavelength λ of 150-250 nm, and determination of the nitrite concentration from the difference between the concentration values obtained from the extinctions of the non-reduced and the reduced liquid samples.