Electrochemical Sensor for Caffeine in Coffee and Beverages Using a Naphthalene Sulfonic Acid Polymer Film–Based Modified Electrode

Abstract

A polymer film–modified electrode for caffeine determination by electrooxidation has been developed by electropolymerising 7-amino-4-hydroxynaphthalene-2-sulfonic acid on a glassy carbon electrode. Comparison of the response at the bare and modified electrodes using cyclic and differential pulse voltammetry showed the electrocatalytic effect of the polymer film in reducing the potential needed for caffeine oxidation, as well as increasing the current response signal. Under optimised conditions, this simply prepared modified electrode led to detection and quantification limits of caffeine of 0.23 µM and 0.78 µM, respectively, and a linear dynamic range of 10–500 µM. The developed method also showed excellent repeatability and reproducibility in addition to operational stability, with no significant change in response after fifty continuous measurements. The performance of the electrode was successfully demonstrated by analysing the caffeine content in instant coffee and in commercial beverages.