We present spectrograms of the central stars of the planetary nebulae IC 3568, IC 4593, NGC 6826, NGC 6543 and NGC 6572, obtained at La Palma, using the Intermedíate Dispersión Spectrograph and a CCD detectors attached to the Cassegrain focus of the 2.5m Isaac Newton telescope. We obtained a spectral resolution of 0,6 Angstroms. We have searched for spectral and radial velocity variations and we have made, whenever possible, a quantitative spectroscopic analysis of the photospheric line profiles. Besides, we have found that the nebular He II emission at 4686 Angstroms in the spectrum of NGC 6572 is stronger than 20 years ago. This may imply an increase in the effective temperature of the central star.