Quantification of caffeine in dietary supplements and energy drinks by solid-surface fluorescence using a pre-concentration step on multi-walled carbon nanotubes and Rhodamine B

Abstract

A new method for the determination of caffeine, a non-fluorescent analyte, based on the enhancement of the fluorescence of Rhodamine B dye on a membrane filter modified with multi-walled carbon nanotubes is proposed. The method comprises the preconcentration of caffeine on solid support by chemofiltration in buffered solution onto multi-walled carbon nanotubes previously oxided and dispersed in a cationic surfactant admicelles. The effect of experimental parameters, included buffer nature and pH, solid support nature, filtration flow rate, dye and carbon nanotubes concentration, surfactant nature and concentration were investigated by means uni-variation assays. At the best experimental conditions, the preconcentration system provided the detection and quantification limits of is 0.3 µg L-1 and 1.1 µg L-1, respectively. A wide linear range varying from 1.1- 9.7x103 µg L-1 concentration (r2 = 0.999). The satisfactory recovery values obtains using standard addition method confirms the feasibility of this method for caffeine determination in energizing dietary supplements and energy drinks.