Potentiometric sensor, based on ionic pair tetraoctadecylammonium tetraphenylborate (TODA-TPB) used as a sensing material and o-nitrophenyl octyl ether (\( \mathit{o} \)-NPOE) as a plasticizer, was used for determination of anionic surfactants. There was 3 % of sensing material in the sensor membrane. Six different internal electrolytes (sodium chloride, lithium chloride, sodium dodecyl sulfate, sodium tetraphenylborate, sodium acetate and potassium chloride) were analyzed on two concentration levels. Potentiometric titrations of sodium dodecyl sulfate (NaDDS), \( \mathit{c} \) = 4 ∙ \( 10^{-3}\) M were preformed using 4 ∙ \( 10^{-3}\) M cetylpyridinium chloride (CPC) and TODA-TPB sensor as an indicator for end point of titration. The highest potential jump of 410.8 mV in a titration curve for NaDDS was observed using 3 M NaCl as a internal electrolyte. After potentiometric titrations, TODA-TPB sensor response characteristics toward 5 ∙\( 10^{-5}\) M NaDDS were tested using six different electrolytes on two concentration levels, preforming tests in water with pause; in water without pause and in 0.01 M \( Na_{2}SO_{4}\) with pause. Results depend on nature and concentration of internal electrolyte. Slope and low detection limit were parameters for choosing the best internal electrolyte. Best results were obtained using 3 M NaCl as internal electrolyte in sensor. TODA-TPB sensor with 3 M NaCl as inner electrolyte revealed Nernstian slope (-58.0 ± 0.9 mV/decade of activity) and low detection limit (1.0 ∙ \( 10^{-7}\) M) for DDS anion in water without pause between measurements. Sensor lifetime was six months. Thesis contains a part with teaching method on subject Soaps and detergents.