The research associated with this work centres on the development and synthesis of selective ionophores that are capable of detecting potassium phosphate ions in aqueous solutions. This specific detection of K+ ions that are bound to a phosphate ion is crucial because both ions play a leading role in water pollution. This work describes a K+ ion-sensing system using a potentiometric method based on macrocyclic compounds. This thesis consists of six chapters. Chapter one includes a short history and introduction of the electrochemical sensors with a description of macrocyclic compounds as ionophores which are related to this thesis work. The second chapter describes the experimental techniques which have been used to synthesize the target compounds including single-crystal X-ray structural analysis. Synthesis a novel ionophore ((((3,4,5-trinitro-1,2-phenylene)bis( oxy))bis( ethane-2, ldiyl))bis( oxy))bis( ethane-2, l-diyl) dinitrate based on open ring macrocyclic compound structure and the synthesis and performance of ten ionophores for the electrode potentiometric applications within a PVC membrane is conveyed in chapter three. The characterisations of the those ionophores are reported including FT-IR data, 1H NMR,13C NMR, HSQC NMR, 2D NMR including COSY NMR, Mass spectrometry, and single-crystal X-ray structural analysis for confirming the closing ring structures. Those ionophores are 4-nitro benzo-15-crown-5 (1), 4-amino benzo15-crown-5 (3), dinitro benzo-15-crown-5 (2), diamino benzo-15-crown-5 ( 4), 4nitro benzo-18-crown-6 (5), 4-amino benzo-18-crown-6 (8), dinitro benzo-18-crown6 ( 6), diamino benzo-18-crown-6 (9), dinitro dibenzo-18-crown-6 (7), diamino dibenzo-18-crown-6 (10). In addition to that another five ionophores have been applied within a PVC membrane which there were 1-aza-18-crown-6, benzo-15crown-5, benzo-18-crown-6, dibenzo-18-crown-6, and dicyclohexyl-18-crown-6 is reported in this chapter. The ability to synthesis these ionophores are important to enable a review of the effects of both the ring size and the associated functional groups. Chapter four describes the data of the effect of a range of plasticisers for incorporating the ionophores into the membrane for optimum sensor design. Those plasticisers are dibutyl phthalate, 2-nitrophenyl phenyl ether, dioctyl phenyl phosphonate, dioctyl phthalate, and bis (2-ethylhexyl) adipate. The thermal properties of all blends are studied by TG/DSC. The assessment of the designed electrode is applied in chapter five which includes the modified electrodes with the ionophores dibenzo-18-crown-6 proving to be the most effective with a shelf life of 40 days; this ensemble also showed negligible drift. It responded in a near Nemstian fashion, and showed a low detection limit of 3.2 x 1 o-6 mol L-1, and a fast response time of 30 seconds over a concentration range of 5 x 10-5 mol L-1 to 1 x 10-1 mol L-1• The morphologies of the sensor after using it is studied by imaging of the sensor in scanning electron. While the energy-dispersive X-ray spectroscopy is used to gather data about the elemental composition of the samples' surface. X-rays, which are characteristic for different elements and a composition spectrum is produced. Finally, chapter six includes conclusions of the thesis work which involves that the resulting electrode signifies a significant advancement in the construction of a potentiometric device for the determination of potassium phosphate concentrations in solution and suggestions for future work.