The main component of the ion selective surfactant sensor is the sensing membrane. Ion selective sensing membranes are usualy fabricated as a liquid type membrane with matrix made of a PVC, ionophore and a plasticizer. Plasticizers soften the PVC but due to their liphopilicity they influence the ionophore, the ion exchange across the membrane, membrane resistance and consequently the analytical signal. The aim of the research was to investigate the influence of four different plasticizers on the analytical properties of the surfactant sensor membrane towards cationic surfactants. 1,3-didecyl-2-methyl-imidazolium-tetraphenylborate (DMI-TPB) ion exchange complex was used as an ionophore. Two cationic surfactants; cetylpyridinium chloride (CPC) and hexadecyltrimethylammonium (CTAB), were used to measure the membrane response characteristics for all plasticizer formulations. Next, the same membranes were used to perform the titrations of the CPC and CTAB with dodecyl sulfate (DS) as a titrant. The plasticizer with the best analytical properties was selected for testing on real samples of six pharmaceutical disinfectants. The results were compared with standard surfactant sensor.