We plan to present the first, preliminary results of a pilot study conducted with GTC devoted to test the reliability of OSIRIS TFs to determine radial velocities by mapping in wavelength strong absorption lines, like e.g. the Ca triplet lines. The ultimate goal of this pilot project is to measure the velocity field of the globular clusters around VCC1261, a dwarf elliptical in the Virgo cluster, for which Keck spectroscopic data is already available.