الفهرس 
General IntroductionOnly 14 pages are availabe for public view
 |  | from | 153 |  |  |
| | | from | 153 | | |
Abstract
- The thesis content can be portrayed briefly as four chapters:
➢ Chapter(I): General introduction:
- This chapter discusses main points in potentiometric sensors field like: history of ISEs, components of ISEs and their functionalities, characteristics of potentiometric ISEs, solid state electrodes (their advantages over conventional electrodes, mechanism of response, the advantages and disadvantages or limitations for both types of electrodes), recent technologies and trends used in potentiometric electrodes for analytical analysis.
➢ Chapter (II): Potentiometric detection of low-levels of sulfamethazine in milk and pharmaceutical formulations using novel plastic membrane sensors.
In this chapter Novel potentiometric sensors for selective screening of sulfamethazine (SMZ) in pharmaceutical preparations and milk samples were reported. Sensor membranes were made from PVC matrix doped with magnesium (II)-, manganese (II)- and dichlorotin (IV)-phthalocyanines as ionophores and aliquate-336 and Nitron/SMZ ion-pair complex as an ion exchangers. These sensors revealed fast, stable and near-Nernstian anionic response for the singly charged sulfamethazine
anion over the concentration range (10-2-10-5) M. The sensors exhibited good selectivity towards SMZ over most known anions, excipients and diluents commonly added in drug preparations. Validation of the proposed methods was demonstrated via evaluating the detection limit, linear response range, accuracy, precision (within-day repeatability) and between-day-variability. The sensors were easily interfaced with a double
xv
Summary
channel flow injection system and used for continuous monitoring of SMZ in drug formulations, spiked milk samples and biological tissues. The method offers the advantages of design simplicity, results accuracy, and automation feasibility.
➢ Chapter (III): Novel potentiometric 2,6-dichlorophenolindophenolate
(DCPIP) membrane-based sensors: Assessment of their input in the determination of total phenolics and ascorbic acid in beverages
In this chapter, we demonstrated proof-of-concept for the use of ion-selective electrodes (ISEs) as a promising tool for the assessment of total antioxidant capacity (TAC). Novel membrane sensors for 2,6-dichlorophenolindophenolate (DCPIP) ions were prepared and characterized. The sensor membranes were based on the use of CuII-Neocuproin/2,6-dichlorophenolindophenolate ([Cu(Neocup)2][DCPIP]2) (sensor I), or methyleneblue/2,6-dichlorophenolidophenolate (MB/DCPIP) (sensor II) ion association complexes in plasticized PVC matrix. The sensors revealed significantly enhanced response towards DCPIP ions over the concentration range 5.13x10-5-10-2 and 5.15x10-5-10-2 M at pH 7 with detection limits of 6.3 and 9.2 µg/mL with near-Nernstian slope of -56.2±1.7 and -51.6±2 mV/decade for sensors I and II, respectively. Effect of plasticizers and various foreign common ions were also tested. The sensors showed enhanced selectivity towards DCPIP over many other phenolic and inorganic ions. Long life span, high potential stability, high reproducibility, and fast response were also observed. Method validation was also verified by measuring the detection limit, linearity range, accuracy, precision, repeatability and between-day-variability. The sensors were introduced for direct determination of TAC in fresh and canned juice samples collected from local markets. The
xvi
Summary
obtained results agreed fairly well with the data obtained by the standard method.
➢ Chapter (VI): Non-equilibrium potential responses towards
neutral orcinol using all solid-state potentiometric sensor integrated with molecularly imprinted polymers.
Molecularly imprinted polymer (MIP) receptors have been synthesized, charcterized and applied as new selective receptors in solid-contact ion selective electrodes (ISEs) towards un-dissociated 3,5-dihydroxy toluene (orcinol). Two monomers, namely methacrylic acid (MAA) and acrylamide (AA) were used in the preparation of MIP receptors. Graphen (Gr) was used as the solid contact material between the sensing membrane and the electrical contact substrate. Based on non-equilibrium sensing mechanism the proposed sensors reveal observably enhanced detection sensitivity towards orcinol with detection limits of 1.7x10-5 and 3.3x10-6 M for sensors based on MIP/MAA and MIP/AA, respectively. The selectivity coefficients measured by the modified separate solution method (MSSM) for the proposed sensors showed good selectivity towards orcinol over most common other phenols and inorganic anions. All measurements were made in presence of 30 mM phosphate buffer solution (PBS) with a pH of 7.0. Potential stability for the proposed sensors was tested by constant-current chronopotentiometry technique. No water films were formed between the ion-selective membrane and the electron conductor substrate. The applicability of MIP/MAA incorporated ISE has been checked by recovery test of orcinol in the presence of soil matrix and by standard addition method.