Simultaneous analysis of vitamins and caffeine in energy drinks by surfactant-mediated matrix-assisted laser desorption/ionization

As a new approach to rapid small-molecule analysis, surfactant-mediated matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI–TOF-MS) was successfully used in the analysis of caffeine and the vitamins riboflavin, nicotinamide, and pyridoxine in various energy drinks. Of five common MALDI matrices tested (α-cyano-4-hydroxycinnamic acid, sinapinic acid, 2,5-dihydroxybenzoic acid, dithranol, and 2′,4′,6′-trihydroxyacetophenone), α-cyano-4-hydroxycinnamic acid was found to be most suitable for analysis of high-sugar-containing energy drinks. Cetyltrimethylammonium bromide (CTAB) surfactant was used as a matrix-ion suppressor, at a matrix:surfactant mole ratio of approximately 500:1. The resulting mass spectra show very few matrix-related ions, while analyte signals were clearly observed. For comparative purposes the same analytes were identified and quantified in energy drinks by LC–ESI–MS with UV detection. Quantitatively the calibration curves of all four analytes showed a marked improvement when the surfactant-mediated method was used compared with traditional MALDI–TOF-MS; correlation coefficients of 0.989 (nicotinamide), 0.991 (pyridoxine), 0.983(caffeine) and 0.987 (riboflavin) were obtained. It was found that in quantitation of the energy drink analytes the surfactant-mediated MALDI–TOF-MS results were comparable with those from LC analysis. In reproducibility experiments RSD values ranged from 9.7 to 18.1%. The work has demonstrated that this mass spectrometric approach can be used as a rapid screening technique for fortified drinks.