**5. Conclusion**

There are several considerations in the optimization of a transdermal drug delivery system. The choice and design of polymers, adhesives, penetration enhancers and plasticizers in transdermal systems are crucial for drug release characteristics as well as mechanical properties of the formulation. Beside the other components of transdermal patches, plasticizers also significantly change the viscoelastic properties of the polymers. The reasons for the use of plasticizers in transdermal drug delivery systems are the improvement of film forming properties and the appearance of the film, preventing film cracking, increasing film flexibility and obtaining desirable mechanical properties. Therefore, the selection of the plasticizer type and the optimization of its concentration in the formulation should be carefully considered.

#### **6. References**


The characterization of the cellulose membranes where polyethylene glycol 600 has been used as plasticizer has been made and it has been determined that, besides the plasticizer concentration, preparation temperature was also effective on the membrane properties. It has been determined that, the membranes prepared at 40°C were more homogeneous and the diffusion of the active substance scopolamine, has realized through 3 days, controlled and constant, from the membranes containing 10% or 20% polyethylene glycol 600. It has been reported that, in order to improve the mechanical properties of the cellulose acetate membranes and to enable the linear release of the active substance, polyethylene glycol

There are several considerations in the optimization of a transdermal drug delivery system. The choice and design of polymers, adhesives, penetration enhancers and plasticizers in transdermal systems are crucial for drug release characteristics as well as mechanical properties of the formulation. Beside the other components of transdermal patches, plasticizers also significantly change the viscoelastic properties of the polymers. The reasons for the use of plasticizers in transdermal drug delivery systems are the improvement of film forming properties and the appearance of the film, preventing film cracking, increasing film flexibility and obtaining desirable mechanical properties. Therefore, the selection of the plasticizer type and the optimization of its concentration in the formulation should be

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**5. Conclusion** 

carefully considered.

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**6** 

*Egypt* 

Mohsen M. Zareh\*

*Zagazig University, Zagazig* 

**Plasticizers and Their Role in** 

*Department of Chemistry, Faculty of Science,* 

**Membrane Selective Electrodes** 

**E = E + (RT/ZF) ln a** (1)

E = RT/ZxF ln (ax/aA) = const + S log (ax) (2)

In the last four decades, the uses and application of ion-selective electrodes was widely applied in several researches as well as analytical projects. These electrodes are varied between solid state electrodes, liquid membrane electrodes, gas membrane electrodes, and plastic membrane electrodes. Plasticizers are one of the major components of the plastic

In the beginning, a general idea about ion-selective membrane electrodes (Janata *Principles of Chemical Sensors* 1989) will be useful to understand the role of plasticizers as they are part of the constituents for some of them. These membranes are the main component of the potentiometric ion sensors. They are responsible of forming a type of discrimination in the electrode behavior towards one ion rather than others. A potential difference will be aroused when the analyte ion can penetrate across the phase boundary between the two phases (analyte solution, and internal reference solution). Accordingly, an electrochemical equilibrium will be formed, due to different potentials at both sides of the membrane. The

Where, E : is the standard cell potential, R: general gas constant, Z: valency of the analyte

If the activity of the target ion at side A is kept constant, the unknown activity at side B (aA =

There are two main groups of membranes, which are used in ion-selective electrodes: namely, crystalline and noncrystalline membranes (Buck and E. Lindner, *Pure &* 

membranes. As it is usually known, they are responsible of their physical properties.

potential difference (E) across the membrane is described by the Nernst equation:

ax) is related to (E) by the following equation (at equilibrium condition):

ion, F:Faraday's constant, a: activity of the analyte ion.

where S=59.16/Z [mV] at T=298 K.

*App.Chem.* (1994).

\*Corresponding Author

**1. Introduction** 

