Ion-selective electrodes of the coated-wire type were used in potentiometric titrations of polypropylene glycols, copolymers of ethylene oxide and propylene oxide and non-ionic surfactants based on oxyalkylated fatty alcohols and furfurylalcohol. The titration with a standard solution of sodium tetraphenylborate is based on precipitation of ternary compounds in the presence of bivalent metal ions; barium(II) salts are preferable. This compound is extractable to the membrane plasticizer; the electrode potential is than governed by the extraction principles. The signal-stabilization time during titrations depends on the length of the poly(oxypropylene) chain and thus, the results of manual titrations are more precise than those of automatic titrations. Moreover, the results indicate that an average of 6.2 oxypropylene units correspond to one tetraphenylborate ion, ie, 12.4 units per each barium(II) ion. For analysis of detergents or other samples of practical importance, the use of empirical titration equivalents is recommended.