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), mean error, confidence limit for concentration, and confidence limit for potential.
The electrodes (A,B and C) based on DBP, TBP and ONPOE respectively, gave a same linear range from 1x10-1 to 1x10-4 M but for electrode D based on DBPH gave the linear range from 1x10-1 to 5x10-4 M. The slopes are (40.58, 39.82, 51.52 and 56.17) mV/decade, with the correlation coefficients are (0.9984, 0.9988, 0.9991 and 0.9993), and the limit of detection 3.5x10-5, 5x10-5, 5.5x10-4 and 2x10-4 M respectively. The pH range was (2.4-8.4), (1.5-6.4), (3.0-7.3) and (4.1-6.8) respectively, and the lifetime were about (~29 days, ~23 days, ~2 days and ~72 days) respectively. The relative standard deviation (RSD%) was (0.662, 0.802, 0.414 and 0.287) respectively.
The stability of the four electrodes was monitored continuously and evaluated; the standard deviation of potential drift obtained = (±3, ±4, ±9 and ±1) mV/day for membranes (A, B, C and D) respectively. The influence of inorganic cations such as (Li+, Na+, K+, Mg+2, Ca+2, Zn+2, Al+3, Fe+3, Cr+3) for the electrodes (A, B, C, and D) was studied by using separation and match methods to determine the selectivity potential coefficient KpotA,B. It was found that the electrodes (D) based on DBPH plasticizer gave excellent results; so, it has been chosen as the best combination of plasticizer and electro-active compound.
The practical utility of the electrode has been demonstrated by using it's as indicator electrode in potentiometric precipitation titration of promethazine hydrochloride solution with phosphotungistic acid solution and with hydroquinone solution. Standard addition method and multi standard addition method have been also successfully applied and presenting an excellent results.
The proposed electrode was successfully applied to the determination of promethazine hydrochloride in pharmaceutical preparation (Phenergan). The analytical method proposed proved to be a simple, rapid and good accuracy.
