title: 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 pre-concentration of caffeine on a solid support by chemofiltration in buffered solution onto multi-walled carbon nanotubes previously oxidised and dispersed in cationic surfactant admicelles. The effect of experimental parameters, including the nature of the buffer and pH, the nature of the solid support, filtration flow rate, dye and carbon nanotube concentration, and the nature of the surfactant and concentration were investigated by means univariation assays. Under optimum experimental conditions, the pre-concentration system gave detection and quantification limits of 0.3 and 1.1 µg l(-1), respectively. A wide linear range was achieved varying from concentrations of 1.1 to 9.7 × 103 µg l(-1) (r(2) = 0.999). Satisfactory recovery values were obtained using the method of standard addition, confirming the feasibility of this method for caffeine determination in energising dietary supplements and energy drinks.
authors.affiliation: a Área de Química Analítica, Facultad de Química, Bioquímica y Farmacia , Universidad Nacional de San Luis , San Luis , Argentina.
authors.forename: María Carolina
authors.initials: MC
authors.lastname: Talio
authors.forename: María Gimena
authors.initials: MG
authors.lastname: Acosta
authors.forename: Magdalena
authors.initials: M
authors.lastname: Alesso
authors.forename: Marta O
authors.initials: MO
authors.lastname: Luconi
authors.forename: Liliana P
authors.initials: LP
authors.lastname: Fernández
mesh_terms: D001628:Beverages / Q000032:analysis*; D002110:Caffeine / Q000032:analysis*; D002138:Calibration; D019587:Dietary Supplements / Q000032:analysis*; D037742:Nanotubes, Carbon; D015203:Reproducibility of Results; D012235:Rhodamines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods*
chemical_list: D037742:Nanotubes, Carbon; D012235:Rhodamines; D002110:Caffeine; C029773:rhodamine B
keywords: Rhodamine B; caffeine monitoring; multi-walled carbon nanotubes; nylon membranes; solid-surface fluorescence