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 (alpha-cyano-4-hydroxycinnamic acid, sinapinic acid, 2,5-dihydroxybenzoic acid, dithranol, and 2',4',6'-trihydroxyacetophenone), alpha-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.