Spectrohotometric observations at high signal-to-noise ratio for a sample of 62 planetary nebulae are presented, together with the plasma and abundance analyses. The objects were selected homogeneously from the `Strasbourg-ESO Catalogue of Galactic Planetary Nebulae' by their height above the disk (over 300pc) and their H{beta} surface brightness (between 10^-12^ and 10^-14^mW/m^2^/arcsec^2^). The abundances of O, S, Ar, and Cl are tighly correlated. The N/O ratio shows a wide range of values, independent of He or O abundance.