The stimulating and performance-enhancing properties of caffeine are often explored in one the most consumed types of supplements: the pre-workout supplements (PWS). However, despite the popularity of PWS, previous studies have reported incompatibilities between what is described in their labels and their actual caffeine content. This study aimed to develop, to optimize, and to validate a gas-chromatography coupled to nitrogen-phosphorus detector (GC-NPD) method to quantify caffeine in PWS and to analyze commercial PWS marketed in Brazil to estimate the caffeine daily intake. For this purpose, three different extraction procedures were evaluated: agitation in vortex, shaker, and sonication. Sonication yielded the best extraction results. Next, the parameters' temperature and time were optimized by using central composite rotatable design (CCRD) and response surface methodology, which revealed the optimal values of 70°C and 10 min. The method was validated and applied to quantify caffeine in 52 PWS. From the 36 PWS labels that specified the caffeine amount, seven (19%) presented more than 120% of the declared quantity, whereas 15 (42%) contained less than 80% of the labeled caffeine. Additionally, six products presented undeclared caffeine. Considering the label stated doses, five supplements exceeded the safe caffeine daily intake (400 mg). On the basis of these findings, supplement quality control remains an issue that deserves more attention from consumers, manufacturers, and regulatory agencies. Finally, we suggest that PWS consumers be careful of the habit of ingesting caffeine through other sources and avoid ingesting two or more different PWS products in the same day.
Keywords: GC-NPD; caffeine daily intake; dietary supplements; label information; multivariate optimization.
© 2021 John Wiley & Sons, Ltd.