New expressions for the ON and NS calibrations (ON11 and NS11 calibrations) for the determination of oxygen and nitrogen abundances in H II regions are proposed. New criteria to divide the H II regions into three classes (hot, warm and cold) are also suggested. The ON11 and NS11 calibrations provide more accurate abundance determination from global spectra in comparison to the ON and NS calibrations. The O and N abundances are estimated for a sample of 57470 SDSS galaxies using the ON11 and NS11 calibrations. The strong line flux measurements for the SDSS spectra of those galaxies are taken from the MPA/JHU catalogue. A mass — metallicity diagram for several redshift ranges are constructed. It is found that the interstellar medium of galaxies with high masses lg(M/M_☉) > 11.3 was not enriched in both oxygen and nitrogen during the last 4 Gyrs (corresponding to the redshift interval z = 0 — 0.4). This indicates that the significant star formation in those galaxies was completed more than 4 Gyrs ago. For galaxies of lower masses, the changes in oxygen and nitrogen abundances increase with decreasing the mass of a galaxy for the time under consideration.