The first, we describe simultaneous voltammetric determination of penicillamine (PA) in the presence of uric acid (UA) using a paste electrode(PE) that is consist of p-aminophenol as a mediator and multiwall carbon nanotubes with TiO 2 nanoparticle for rapid, sensitive, and highly-selective determination. The electrochemical behavior of the compounds at this modified electrode was studied by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The results indicated that the chemically modified electrode exhibits efficient electrocatalytic activity in the oxidation of PA which occurs at a potential of about 530 mV, less positive than that for the unmodified carbon nanotubes paste electrode at pH 6.0. PA and UA in a mixture can be measured independently from each other with a potential difference of 215 mV using DPV.The kinetic parameters such as electron transfer coefficient, ?=0.38 and catalytic reaction rate constant, K h =2.58×10 3 M –1 s –1 were also determined using electrochemical approaches. The diffusion coefficient for PA at the surface of p-aminophenol-modified carbon nanotubes–TiO 2 paste electrode was determined 7.14×10 -5 cm 2 s ?1 . Finally, the sensor was examined as a selective, simple, and precise new electrochemical sensor for the determination of PA in real samples with application standard addition method in drugs and urine. Finally, a sensitive and selective electrochemical method for the determination of isoproterenol (ISPT) was developed by using a ferrocene-multiwall carbon nanotubes paste electrode (FCMWCNTPE). The fabrication of FCMWCNTPE and its electrocatalytic effect for the electrochemical oxidation of ISPT were investigated by electrochemical impedance spectroscopy and voltammetric methods. The cyclic voltammetric results indicate that multiwall carbon nanotubes remarkably enhance the oxidation of ISPT at pH 5.0, which is leading to considerable improvement of anodic peak current for ISPT, and allow the development of a highly sensitive voltammetric sensor for determination of ISPT in pharmaceutical and urine samples. It has been found that under the optimum condition (pH =5.0,) in cyclic voltammetry, the oxidation of ISPT occurred at a potential about 140 mV less positive than that unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient and catalytic reaction rate constant, were also determined and they were equal.0.75 and 124.05767 M –1 s –1 . Finally, differential pulse voltammetry exhibited two wide linear dynamic ranges and a lower detection limit of 0.07 µmol L -1 for ISPT