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Abstract The present thesis describes the preparation and determination of the characteristic performance of screen printed electrodes for the possibility of rapid in field analysis. These electrodes are utilized for the determination surfactants such as dodecyltrimethylammonium bromide (DTAB), cetylpyridinium chloride (CPC), and Septonex (1-(ethoxycarbonyl) pentadecyltrimethylammonium bromide) in pharmaceutical preparations and sea water. The electrode cocktail consists of paste composed of a mixture of graphite powder (1-2 μm), plasticizer and binder. Potentiometric titrations of the surfactants under investigation are based on ion pairs formation between the analytes and the titrant materials (sodium tetraphenylborate (NaTPB), phosphotungstic acid (PTA), phosphomolybdic acid (PMA), silicotungstic acid (STA) and ammonium reineckate (RN) which has an opposite charge where precipitation of an ion pair of limited solubility in water is observed. The thesis contains three chapters: Chapter I It includes introduction. General introduction concerning the theoretical bases for preparation and uses of the different types of ion selective electrodes is described. Focusing on screen-printed carbon paste electrode, as regards of methods of preparation, general properties of screen-printed electrode and uses of this surface electrode in the potentiometric titration of different species, is given. Also, a literature survey on the different methods used for the determination of dodecyltrimethylammonium bromide (DTAB), cetylpyridinium chloride (CPC) and sodium dedecylsulphate (SDS) are discussed in details. These methods include spectrophotometric, capillary electrophoresis, ion-selective, chromatographic, polarographic and other miscellaneous methods. On screening literature survey, it was obvious that no previous work has been done using screen printed electrodes for the determination of surfactants except one publication given by the author. SUMMARY 137 Chapter II It contains full details for the preparation of all types of ion selective electrodes specially the preparation of the screen-printed electrode and working procedures. The analytical methods used to evaluate surface activity of specific materials, evaluation of the electrode selectivity, determination of the studied surfactant in pure solution and in some commercial preparations are also described. Chapter III-V Screen-printed ion-selective electrode for the determination of cetylpyridinium chloride (CPC) is presented. These new electrodes involve in situ, modified and unmodified screen-printed ion selective electrodes for the determination of CPC. For quantitative and qualitative composition, optimization of the developed sensors (PVC, CPE and SPEs), an election scheme was followed. Both unmodified (plain) electrodes and modified (in situ IP formation and modification with IP) electrodes were prepared and tested for nature and content of modifier, type of plasticizer, pH effect, response time and applications. 1. CP-ISEs modified with the IPs 1.1. Effect of the ion pair content The influence of the CP-TPB content (sensing material) on the electrode performance was studied. For this purpose, various electrodes were prepared containing different amounts of the ion pair (5-20 mg for PVC, 5-30 mg for CPE, and 5-30 mg for SPE). It was obvious from that, as the ion-pair content increases, the slope of the calibration curve increases till certain point (optimum IP content is found to be 15, 25 and 20 mg for PVC, CPE, and SPE, respectively) then decreases for all types of the studied electrodes. This is also supported by the high slope values of the calibration curve in the tested concentration range from 10-6-10-2 M (55.90±0.99, 57.23±1.05 and 58.49±0.59 mV/decade for PVC, CPE, and SPE, respectively) SUMMARY 138 1.2. Effect of the ion pair type Different fabricated electrodes (PVC, CPE, and SPEs) were modified in bulk with different IPs; CP-TPB, -RN, -PTA, -PMA or -TSA as electroactive components and conditioned in 10-3 M CPC solution for 24 h for PVC and CPE electrodes. While for SPEs, for preconditioning for only 30 min before performing the calibration process is done. The fabricated electrodes show Nernstian responses towards CPC with different slopes depending on the nature of the IP used. 2. CP-ISEs modified with IPs in situ 2.1. Effect of the counter ion pair agent content The effect of the counter ion-pair agent content on the performance of the PVC, CPE, and SPE electrodes containing 5-25, 10-40, and 20-70 mg of NaTPB as an ion pairing agent were studied. They were prepared and soaked in 10-2 mol L-1 of CPC solution for 30 min. The result obtained showed that 7.5, 32, and 47 mg of TPB contents gave the highest slope values of 64.34±2.16, 60.44±1.98, and 55.28±1.20 mV/decade for PVC, CPE, and SPE, respectively 2.2. Effect of the ion pairing agent type Electrodes containing different ion pairing agents (TPB, RN, PTA, STA, and PMA) were prepared, soaked in 10-2 mol L-1 of CPC for 30 min, and then used for the determination of CPC. 3. CP-ISEs modified with ion pairs by soaking (Plain electrodes): 3.1. Effect of the plasticizer on soaked electrodes performance The influence of the type of the plasticizer on the electrode performances has been studied as the electrode plasticized with o-NPOE is compared with those of TCP, DOP, DBP or DOS. The obtained calibration graphs with SPE using different methods of preparation and different plasticizers clarified that, using of o-NPOE as plasticizer showed the highest sensitivity of the membrane electrode indicated with the highest slope and wider linear range specially with the soaked electrodes. SUMMARY 139 3.2. Effect of the IP solution type Soaking of the unmodified PVC, CPE, and SPE electrodes in freshly prepared IPs suspensions with TPB, RN, PTA, PMA, and STA is carried out where they subsequently used for potentiometric measurements. It is obvious that the electrodes soaked in the CP-TPB ion pair are found to have the highest sensitivity as indicated by the highest slope values. The mass production of disposable potentiometric strips using screenprinting technology is described. The printed disposable electrodes strips containing both the working are utilized as an end point indicator electrode for the potentiometric titration of different surfactants in their pure solutions and different samples. The fabrication of the potentiometric strips and the preparation of the homemade printing carbon ink are described well. The factors affecting the electrode performance are well presented and discussed in details in order to give clear informations about screen printed technology. The analytical performance of the obtained strips is compared with those for CPE, and PVC electrodes using different modes of preparation (modified with IP, modified in situ or soaked) were evaluated according to IUPAC recommendations. The printed strips do not require any preconditioning before application in the potentiometric titration of surfactants and have a very short response time reaching 3 seconds with adequate shelf time (6 months). The influence of pH on the response of the PVC membrane CPE and SPE was checked by recording the potential readings of the cell for solutions containing 10-4- 10-2 M of CPC at different pH values (pH 2-12) indicate that the response of the electrodes was pH independent in the pH range 3.0-7.0, 3.0-8.0 and 3.0-8.0 for PVC, CPE and SPEs, respectively. The proposed disposable strips have been successfully used for the potentiometric titration of the cationic surfactants in their analytical grad solutions, pharmaceutical preparations and water samples with sensitivity comparable with the different modes of preparation (modified with IP, modified in situ or soaked), SUMMARY 140 official method and ability of field measurement with a portable potentiometric titration system. The SPEs modified in bulk with different IPs (septonex- TPB, -RN, -PTA, - PMA or -STA) as electroactive components were prepared and conditioned in 10-3 mol L-1 of septonex solution. SPEs gave reproducible results after preconditioning for only 30 min before performing the calibration process. The influence of the type of the plasticizer on the electrode performances has been studied as the electrode plasticized with o-NPOE is compared with those of TCP, DOP, DBP or DOS. The obtained calibration graphs with SPE using different plasticizers clarified that, using of o-NPOE as plasticizer showed the highest sensitivity of the membrane electrode indicated with the highest slope |