5-Amino-2-mercapto-1,3,4-thiadiazole coated nitrogen-doped-carbon sphere composite for the determination of phenolic compounds

Abstract

This study reports the simultaneous determination of phenolic antioxidant compounds of gallic acid (GA) and caffeic acid (CA). The composite probe was fabricated by electropolymerizing 5-amino-2-mercapto-1,3,4-thiadiazole (p-AMT) on nitrogen-doped carbon sphere (N-CS) modified glassy carbon (GC) electrode. The N-CS was derived by carbonizing poly(o-phenylenediamine) microspheres. The proposed p-AMT@N-CS/GC composite electrode exhibited lower operating voltage, good peak separation of 80 mV (for simultaneous GA and CA oxidation), and a dynamic concentration range detection of GA and CA. The kinetic parameters were calculated as follows: charge transfer coefficients of GA 0.80, CA 0.81 and electron transfer rate constants of GA 9.5 s−1, CA 3.3 s−1. The p-AMT@N-CS/GC composite electrode proved useful in the individual and simultaneous monitoring of GA and CA with wide dynamic concentration range (GA 5–1187 μM and CA 5–2082 μM), high sensitivity (GA 0.0251 μA μM−1 and CA 0.1024 μA μM−1), and low limit of detection (GA 0.58 μM and CA 0.143 μM). The p-AMT@N-CS/GC electrode revealed good interference tolerance ability with common interfering species, such as ascorbic acid, uric acid, hydroquinone, catechol, K+, Na+, Mg2+, Cu2+, Ni2+, NO3−, Cl−, SO42−, and glucose. Under optimized conditions, the p-AMT@N-CS/GC electrode was used in the simultaneous determination of GA and CA in grape juice samples.