In first part of this work, a new thiocyanate selective PVC membrane electrode based on copper(II) bis(benzoylacetone)propylenediimine complex as a new neutral carrier is constructed. The sensor displays a linear response in the working concentration range of the electrode is 8.0 ×10 -7 - 1.0×10 -1 M with near Nernestian slope of -57.4 ± 0.5 mV per decade. The other performances of this electrode are low detection limit of 7.4×10 -7 M, short response time (5-10 s), good repeatability for 3 months and extend working pH range of 1.7-11.5. The proposed electrode is more selective for determination of thiocyanate ion over a wide variety of common anions. The present electrode was successfully applied to the determination of thiocyanate ions in saliva sample solutions of smoker and non-smoker persons. The results compared with the standard spectrophotometric method. There is a quite good agreement between both the potentiometric and spectrophotometric procedures. In second part of this work, A synthesized bis(dibenzoylmethanato) Co(II) complex, (Co(DBM) 2 ), has been used as a novel ionophore for the preparation of a new perchlorate ion selective electrode. The electrode exhibits a Nernstian response over the perchlorate concentration range 8.0×10 -7 to 1.0×10 ?1 M with a slope of 60.3±0.5 mV per decade of concentration. The other performances of this electrode are low detection limit of 5.6×10 -7 M, short response time (? 10 s), good repeatability for at least 2.5 months and extend working pH range of 2.0-9.0. The proposed electrode is more selective for determination of perchlorate ion over a wide variety of common anions. The electrode was used to determine perchlorate in river and tap water and human urine samples with satisfactory results. Good recoveries were obtained in all samples. In third part of this work, a cadmium(II) selective PVC membrane electrode based on 1,2-bis(quinoline-2-Carboxamido)-4-chlorobenzene as a neutral carrier is constructed. The sensor shows a Nernestian response for cadmium ions over a wide concentration range (1.0×10 ?6 to 1.0×10 ?1 mol. L -1 ) with slope of 30.3 ± 0.4 mV decade ?1 . The other performances of this electrode are low detection limit of 8.0×10 -7 M, short response time (? 10 s), good repeatability for 2 months and extend working pH range of 2.4 - 9.0. The electrode was also successfully applied to the direct determination of Cd 2+ in real wastewater sample from a near Isfahan Electroplating Factory. The results show good agreement with AAS method.