In this work we have developed low-cost ion-selective electrodes made from 2 mL disposable syringes equipped with plasticized PVC membranes. The membrane solution was optimized in a way that after solvent evaporation it forms a thin, uniform layer enclosing the tip of the syringe. To test the low-cost, easy and fast to prepare alternative to standard commercial sensors, we have chosen the most selective and well-studied ionophore -valinomycin. Characterization of the system in model solutions provided comparable results to sensors assembled using commercial electrode bodies. However, quantification of potassium in real samples, showed, as expected, that measurement in complex, more concentrated solutions of higher ionic strength, such as beetroot soup, tomato-based food products, dried fruits are reproducible but subject to relative error up to 76 %.