Ion-selective electrodes were optimized for the determination of Na⁺, ^K+ and Ca²⁺ in wood pulp suspension. The electrodes were based on solvent polymeric membranes (plasticized PVC) containing neutral carriers. The results obtained with the optimized electrodes were compared to those obtained with commercially available ion-selective electrodes including glass electrode for Na⁺ and solvent polymeric membrane-based electrodes for K⁺, Ca²⁺ and Cl^-. Additionally, commercially available glass electrodes for pH, as well as a solid-state membrane electrode for Cl^- were used. The free ion concentration of pulp samples obtained by ion-selective electrodes was compared to the total concentrations obtained by ICP-AES and XRF.