Potentiometric measurements using sensors with different content (1 %, 3 % and 5%) of ion pair tetraoctadecylamonium tetraphenylborate (TODA-TPB) as sensing material and \( \mathit{o} \) -nitrophenyl octil eter (\( \mathit{o} \)-NPOE) as a plasticizer were performed. Investigation was carried out in order to determine whether the concentration of the sensing material has an effect on the response characteristics of sensor. The direct potentiometric method was used for investigation of response characteristics of the sensors, while the potentiometric titration was used for conditioning the sensors. Sodium dodecyl sulfate (NaDDS, \( \mathit{c} \) = 5·\( 10^{-5} \) mol/L, \( \mathit{c} \)= 1·\( 10^{-2} \) mol/L) and sodium dodecylbenzene sulfonate (NaDBS, \( \mathit{c} \) = 5·\( 10^{-5} \) mol/L, \( \mathit{c} \)= 1·\( 10^{-2} \) mol/L), were used to measure the response characteristics of the sensors in water and sodium sulfate (\( Na_{2}SO_{4} \), \( \mathit{c} \) = 1·\( 10^{-2} \) mol/L). Potentiometric titration were carried out using NaDDS (\( \mathit{c} \) = 4·\( 10^{-3} \) mol/L) as analyte and cetylpyridinium chloride (CPC, \( \mathit{c} \) = 4·\( 10^{-3} \) mol/L) as titrans. The results of investigation of response characteristics of the sensor showed sub-Nernstian response ranging from -54,2 mV/ decade of activity to -55,8 mV/decade of activity. The lowest detection limit of 5·\( 10^{-8} \) mol / L exhibited sensor with 1 % sensor material. The study found that all three sensors are suitable for determining low concentrations of NaDDS and NaDBS and that there is no significant difference in sensor characteristics with a different concentration of sensing material.