Voltammetric sensors for the simultaneous quantification of natural phenolics in coffee and citrus juices

Phenolic antioxidants of various groups are important nutrients in human diet providing positive health effects. Nevertheless, these effects are dose-dependent that requires the control of natural phenolics contents in their sources. Coffee and citrus juices containing significant amounts of hydroxycinnamic acids and flavanones, respectively, are among most widely consumed beverages all over the world. Electroactivity of phenolics allows application of voltammetric sensors for quantification purposes. Highly sensitive and selective voltammetric sensors for the simultaneous determination of hydroxycinnamic acids (caffeic, ferulic, and p-coumaric acids) and flavanones (hesperidin and naringin) has been developed for the first time using glassy carbon electrodes modified with layer-by-layer combination of polyaminobenzene sulfonic acid functionalized single-walled carbon nanotubes and electropolymerized triphenylmethane dyes (phenol red or aluminon). Polymeric coverages have been obtained in potentiodynamic mode. Conditions of dye's electropolymerization have been optimized using voltammetric response of hydroxycinnamic acids or flavanone mixtures. A well-resolved peaks of caffeic, ferulic, and p-coumaric acids at the electrode with poly(phenol red)- based electrode as well as hesperidin and naringin at the polyaluaminon-modified electrode have been observed. The oxidation currents are significantly increased vs. bare glassy carbon and carbon nanotube-modified electrodes. Both sensors provide highly sensitive response to target analytes in differential pulse voltammetric mode. Selectivity in the presence of other natural phenolics has been achieved. Quantification of hydroxycinnamic acids in coffee and flavanones in orange and grapefruit juices has been successfully realized.