In the first section of this project, the oxidation of isoproterenol (ISPT) has been studied at a modified carbon nanotubes paste electrode using electrocatalytic effect of N-(3,4-dihydroxyphenethyl)-3,5-dinitrobenzamide (DHPB). Isoproterenol is known as catecholamines, which are the important neurotransmitters, and being used for the treatment of neural disorders such as Heart disease. The electrochemical behavior of the isoproterenol at this modified electrode was studied by cyclic voltammetry, square wave voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The modified electrode showed very efficient electrocatalytic activity for the anodic oxidation of isoproterenol, owing to decrease in anodic overpotentials. The results indicated that in the presence of isoproterenol, the anodic peak current of the mediator enhanced. Thus, the measurement of isoproterenol with DHPB is based upon this current enhanced that is proportional with isoproterenol concentration. Some of apparatus and cocentration parameters at pH= 7 for the determination of isoproterenol were optimized. The kinetic parameters such as electron transfer coefficient, diffusion coefficient, and catalytic reaction rate constant, were also determined. Under the optimum conditions, ISPT was measured in the range of 0.3 to 125.0 µM with a detection limit of 0.1 µM. The relative standard deviation (RSD%) for seven successive determination of 1.0 and 20.0 µM ISPT were 1.9% and 1.2%, respectively. The influence of various substances as potentially interfering compounds with the determination of ISPT was studied under the optimum conditions. In order to demonstrate the ability of the modified electrode to the determination of ISPA in real samples, determination of ISPA in injection solution, serum, water and urine samples were examined. In the second section, application of 1-hexyl-3-methylimidazolium hexafluorophosphate, as an ionic liquide, for modification of carbon paste electrode in the presence of TiO2 nanoparticles was studied for determination of benserazide and methyldopa. Benserazide (D, L-serine-2-[2,3,4 (trihydroxyphenyl)methyl]hydrazide) used with levodopa for treatment of Parkinson’s disease. Benserazide is an irreversible inhibitor of peripheral L- aromatic amino acid decarboxylase. Methyldopa [?-methyl-?-(3,4-dihydroxyphenylalanine)] is a catecholamine widely used to treat high blood pressure. Cyclic voltammetry, square wave voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were used as diagnostics and measurement techniques. Some of effective parameter in fabrication of the sensor such as percentage of ionic liquide and TiO2 nanoparticles were optimized. The results showed that the maximum sensitivity was obtained with 10.0% w/w TiO2 and 15.0% w/w IL. Under the optimized conditions, the calibration curves were linear in the concentration range of 1.0 to 600.0 µM benserazide, with a limit of detection of 0.2 µM and 0.5 to 345.0 µM methyldopa with a limit of detection of 0.2 µM. The relative standard deviation for 10.0 µM benserazide and methyldopa were 1.4% and 1.6%, respectively. In order to investigate the influence of various species on the determination of benserazide, a fixed amount of benserazide and methyldopa (5 ?M) was taken with different amounts of foreign species and analyzed with cyclic voltammetry. The results demonstrate the modified electrode has a good selectivity for benserazide and methyldopa.The proposed sensor was successfully used for determination of benserazide and methyldopa in human urine and pharmaceutical product (tablet).