Development and Validation of an Analytical Method by HPLC-DAD for Determination of Caffeine in Products Based on Guarana Extracts (Paullinia Cupana). Braz. J. Pharm. Sci. 2023, 59, https://doi.org/10.1590/s2175-97902023e22106. https://doi.org/10.1590/s2175-97902023e22106.