All the validation results are given in table 2. The average ratio of estimated on actual nitrate content was 99.9+-2.0%, whiich is very good considering that the uncertainty of the analytical method is about 4% . In table 2, the deconvolution error, given by UV-prosoftware , indicates the quantitative difference between the UV-spectra and an equivalent one, rebuilt according to the model with estimate values. the lower this error the better the result.