Solid-phase FT-Raman determination of caffeine in energy drinks

A solid-phase vibrational spectrometry-based methodology (solid-phase Fourier transform-Raman spectrometry, SP-FT-Raman) has been developed for caffeine determination in commercial energy drink samples. The Raman spectra of caffeine, fixed on a C18 solid phase packed into a glass tube of 5 mm i.d., was obtained directly between 3500 and 70 cm−1. In order to quantify caffeine, Raman intensity between 573 and 542 cm−1 corrected using a baseline defined between 580 and 540 cm−1 was used. A repeatability of 3%, as relative standard deviation of five analysis of a 200 mg l−1 concentration, and a limit of detection of 18 mg l−1 were obtained. The SP-FT-Raman procedure provides a sampling frequency of 13.3 h−1, higher than that of liquid chromatography (LC), which was 7.0 h−1. The use of FT-Raman reduces the reagent consumption and waste generation, also minimizing the sample handling. Results obtained by the developed procedure were statistically comparable with those found by a reference LC method.