In this research, two electrochemical sensors fabricated for sensitive and selective determination of phenazopyridine (PAP) and dopamine (DA). The electrochemical behavior of these compounds at the modified electrode were studied by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). In the first work, the modified glassy carbon electrode activated with multiwall carbon nanotubes decorated with MgCr 2 O 4 magnetic nanoparticle (MgCr 2 O 4 -MWCNTs) was used to determine PAP. After optimization of several effective parameters, PAP was determined in the range of 0.05 to 7.5 mM and with detection limit of 0.02 mM. The relative standard deviation (RSD%) for ten successive measurements of 5.0 mM PAP was 1.3%. At the second work, the modified glassy carbon electrode with multiwall carbon nanotubes that decorated with NiFe 2 O 4 magnetic nanoparticles (NiFe 2 O 4 -MWCNTs) was used to determine of DA. This sensor was optimized and used for determination of DA over two dynamic ranges of 0.05-6.0 mM and 6.0-100 mM and with the detection limit of 0.02 mM.RSD for 30.0 µM DA is 1.9%. These modified electrodes showed enhanced electrochemical response and strong analytical activity towards the direct electrochemical oxidation of PAP and DA. The influences of interfering compounds on the selectivity were studied. Finally these modified electrodes were successfully applied to the determination of PAP and DA in biological compounds such as tablet, serum and urine samples.
