The proposed electrode was positioned between two phases of aqueous solutions, the outer one was the sample solution and the other one was the inner reference solution which has a fixed concentration of analytic ion. The potential difference was measured across the membrane of the electrode by using two reference electrodes that were placed in aqueous phase. The prepared electrode was used to determine the POP in the pharmaceutical dosage form and human fluids. The ion-pair complex formation of Propranolol is explained in Figure 1.

RESULT AND DISCUSSION

New membranes were prepared for the determination of POP in the pharmaceutical preparations and human fluids, the characterization of these electrodes based on the ion-pair using different plasticizers were described. The new complex (POP-BPB) was proved by the FTIR spectrum as shown in Figures 2 & 3.

Influence of plasticizers

The effect of the plasticizers on the POP electrode’s response was studied by using three plasticizers which are: Di-butylphthalate (DBPH), Tris (2-ethylhexyl) phosphate (TEHP) and Ortho-nitro phenyl- octylether (ONPOE).

Plasticizers were added to dissolve the ion-pair complex and to set the permittivity of the membrane and the mobility of the ion-exchanger in order to give the prepared electrode, the best selectivity and sensitivity [12].

First electrode for POP drug

This electrode consisted of (POP-BPB) as ion pair, DBPH as plasticizer and PVC as supported which dissolved in THF solvent. The calibration curve for the first electrode was plotted between concentrations range (1×10^-6-1×10^-2) M of POP drug and the measured potential for each concentration. The statistical treatments of the measured potential are listed in Table 1.

Second electrode for POP drug

The second electrode was prepared from (POP-BPB) as ion pair, TEHP as plasticizer and PVC as supported which dissolved in THF solvent. The calibration curve for the second electrode was plotted between concentrations range (1×10^-6-1×10^-2) M of POP drug and the measured potential for each concentration. The statistical treatments of the measured potential are listed in Table 2.

Third Electrode for POP Drug

This electrode was synthesized from (POP-BPB) as ion pair, ONPOE as plasticizer and PVC as supported which dissolved in THF solvent. The calibration curve for the third electrode was plotted between concentrations range (1×10^-6 -1×10^-2) M of POP drug and the measured potential for each concentration. The statistical treatments of the measured potential are tabulated in Table 3.

Influence of pH

The effect of pH on the electrode’s potential was evaluated by measuring the potential of the cell at the conc. of (1×10^-4 and 1×10^-3) M of POP solution. The adjustment of the pH was made by adding some drops of (0.1) M hydrochloric acid or sodium hydroxide. At the low pH level, the potential of the electrodes increased, this is because the electrode has responded to the H⁺ ions. While at high pH levels, the potential of the electrodes dropped sharply because of the poisoning of the membrane by the formation of the white precipitation. From Figures 4-6 it can be noticed that POP electrodes do not respond to pH changes in the range [4-8].

Response time and life time

The response time of the electrode can be defined as the time required for the electrode to reach a stable potential after immersing the proposed electrode and the reference electrode in (1×10^-6 and 1×10^-2) M of POP solution. The proposed electrodes gave steady potentials after (1), (0.8) and (0.9) min at (1×10^-2) M and after (3), (3.8) and (4.5) min at (1×10^-6) M for electrode A, B and C respectively. The lifetime of the three electrodes was measured and it was (21), (42) and (1) day for electrode A, B and C respectively. After this time the slope tends to be decreased and the detection limit tends to be increased because of the leaching of the ion pair from the membrane to the external solution (Table 4).

Selectivity

The interferences of some inorganic cations such as: (Li+, Na+, K+, Mg+2, Ca+2, Zn+2, Al+3, Cr+3 and Fe+3) were studied using the separate solution method (SSM) and the Match potential method (MPM). The selectivity coefficient values by (SSM) were calculated by Nickolsky-Eisenman equation and tabulated in Table 5.

Low values of selectivity coefficients were obtained which means no interfering of these cations on the electrode B response.

CONCLUSION

In this study, the constructions of new three electrodes of POP were based on poly (vinyl chloride) (PVC) membrane. It contains the ion-exchanger that formed between POP and BPB, using three different plasticizers: (DBPH), (TEHP) and (ONPOE). It was a sensitive, precise, rapid and inexpensive method which was used in the determination of POP in the pure form, pharmaceutical preparations and human fluids. The electrode B has shown a good performance with the time stability up to (42) days.

• 
  Table 1
• 
  Table 2
• 
  Table 3
• 
  Table 4
• 
  Table 5