We analyze the dielectric properties of the liquid crystal M5 used to investigate the electrohydrodynamics instability in nematic liquid crystals. We show that the spectra of the electrical impedance of doped samples of M5 with several concentrations of salt and of acid can be interpreted by assuming the doped liquid crystal as a dispersion of ions in a dielectric liquid. The analysis has been performed by considering the electrodes as blocking. From the best fit of the experimental data relevant to the real and imaginary parts of the electrical impedance of the cells, we derive the diffusion coefficients for the positive and negative ions and their bulk density. According to our analysis, in the limit of small concentrations of doping substance, the effective dielectric constant of the resulting liquid is, practically, independent of the doping.