Glycine-modified Pencil Graphite Electrode as a Sensor for Caffeine Determination: A Voltammetric Study

Abstract

Background: Caffeine (CAF) is a widely used chemical in foods and pharmaceuticals that is consumed by a lot of people every day. Overconsumption of caffeine can lead to some undesirable symptoms. However, CAF is considered a crucial nervous system stimulant. Aims: This study aimed to find an accurate and effective route for determining caffeine using voltammetric techniques. Objective: In this work, for the first time, a glycine (Gly) modified pencil graphite electrode (Gly/PGE) was used for the determination of caffeine (CAF) by Square Wave Adsorptive Stripping Voltammetry (SWAdSV) technique. Methods: The modification procedure of PGE by Gly was accomplished by performing the cyclic voltammetry (CV) technique for 10 cycles at a potential range of 0.8 to 1.8 V. Moreover, the characterization of Gly/PGE was done by applying the CV technique in aqueous and non-aqueous media and electrochemical impedance spectroscopy (EIS) in addition to the SEM technique. The movement type of CAF toward Gly/PGE was proven to be a diffusion-controlled process by conducting some measurements at different scan rates. The supporting electrolyte for the determination of CAF was studied, where 100 mM of sulfuric acid (H2SO4) provided the best result. Optimization of accumulation time, pulse size, and wave frequency were implemented and found to be 60 s accumulation time, 50 mV pulse size, and 25 Hz wave frequency. The stability of Gly/PGE was studied in different mediums, such as air, ultrapure water, and acetonitrile (CH3CN). Results: The determination of CAF under optimum conditions was within the linear concentration range of 0.1–75 μM, with a correlation coefficient of R2 = 0.9990. The limit of detection (LOD) and limit of quantification (LOQ) were 0.070 and 0.231 μM, respectively. Conclusion: An effective voltammetric methodology was suggested to determine CAF. This methodology has great promise to be applied in different matrices to determine CAF.