Abstract
The determination of chemical abundances in ionized-gas nebulae is based on the detection of auroral emission lines, from which it is possible to deduce the line temperatures of several ions. These lines are weak in low excitation objects, so their measurement is only possible in large aperture telescopes. The GTC would allow us to plan a comprehensive study of chemical abundances in such objects from mid to high resolution spectra, which would give place accurate observational constraints on models of chemical evolution.
