4-Am ino-3 -hydroxynaphthalene sulfonic acid was electropolymerizedrnpotentiodynamically from aqueous solution at the surface of glassy carbon electrodes.rnDifferent Electrochemical and surface characterization techniques like cyclicrn. vo ltammetry, impedance spectroscopy, scanning electron microscopy/energy dispersivernspectroscopy, atomic force microscopy, and x-ray photoelectron spectroscopy were usedrnto characterize the deposited electro active polymer film at the surface of glassy carbonrnelectrodes.rnThe poly(4-Amino-3-hydroxynaphthalene sulfonic acid) modified glassy carbonrnelectrode was further studied as electrochemical sensor for the determination of selectedrnalkaloids (ephedrine, theophylline, and caffeine) and organophosphorus pesticidesrn(fenitrothion and methyl parathion) from real samples using various electroanalyticalrnmethods. The polymer modified electrode showed catalytic effect towards the studiedrnalkaloids and organophosphorus pesticides. For the investigated alkaloids and pesticides,rndetection limits in the range of4.7-79 x 10.8 M and 0.79-1.1 x 10-9 M, respectively werernachieved. In contrast to most of the previous reports on similar alkaloids and pesticides,rnpo ly( 4-Amino-3-hydroxynaphthalene sulfonic acid) modified glassy carbon electroderngave lower detection limits and excellent recoveries making it potentially applicable forrnthe determination of alkaloids and pesticides in environmental samples.rnThe electrochemical behavior of fenitrothion at an electrochemically activated glassyrncarbon electrode was also investigated. The current response showed linear dependence