Disposable Nafion-modified Screen-printed Graphite Electrodes for the Rapid Voltammetric Assay of Caffeine

Abstract

Objective: The aim of this work was the development of Nafion-modified disposable screen-printed graphite electrodes for the voltammetric determination of caffeine and the validation of a method for the rapid voltammetric assay of caffeine in drinks and coffee. Methods: A Nafion-coated screen-printed graphite electrode (fabricated by immersion in a 0.25% (w/v) Nafion solution) was used a working electrode and voltammetry was performed in the differential pulse (DP) mode (initial potential, +0.90 V; final potential, +1.70 V vs. Ag/AgCl (sat. KCl)) in 0.2 mol L-1 H2SO4. Results: Modifying the electrode with a Nafion film improved the sensitivity, the repeatability and the resistance of the electrode towards surface-active compounds. The limits of detection (LOD) and quantification (LOQ) were 0.2 and 0.6 mg L-1, respectively, while the % relative standard deviation (n=8) was 1.3% and 2.8% for 2.0 and 10 mg L-1 caffeine, respectively. The proposed sensors were successfully applied to determine caffeine in samples of energy and cola drinks and instant coffee with recoveries between 97 and 103% and satisfactory agreement with the reference HPLC method. Conclusions: The proposed Nafion-coated screen-printed electrodes are inexpensive and easy to fabricate, disposable, resistant to electrode fouling, do not require activation/cleaning or complex modification protocols and are fit-for-purpose for the task of the rapid voltammetric assay of caffeine.