Electrodes for the determination of promethazine hydrochloride based on PVC membrane were prepared based on the use of ion pair (promethazine-phosphotungstic acid) with the following plasticizers: Di-butyl phosphate (DBP), Tri-butyl phosphate (TBP), O-nitrophenyloctyl ether (ONPOE), and Di-butyl phthalate (DBPH). The properties of these electrodes were studied, including: slope, correlation coefficient, concentration range, detection limit, pH effect, and life time. The statistical treatments were applied for the results that include: relative standard deviation (RSD), relative error (RE),...