This article reports the combined effect of nanoparticles and alignment layers of the cell on the concentration of mobile ions in liquid crystals. Assuming two types of fully ionized species-contaminants in liquid crystal nanocolloids sandwiched between two substrates, several size effects on their electrical properties are modelled. These effects describe the monotonous and non-monotonous dependence of the total concentration of mobile ions on the thickness of the cell and/or on the concentration of nanoparticles. In addition, the tuning of this dependence by varying the concentration of nanoparticles, their size and ionic purity is also discussed. (C) 2017 Elsevier B.V. All rights reserved.