Use of Design of Experiments to Optimize the Chromatographic Separation and Ultrasound-Assisted Extraction for Simultaneous Determination of Methylxanthines and Flavonoids in Guarana

In this work, Design of Experiments and the Derringer’s desirability function were used to optimize the chromatographic conditions and an ultrasound-extraction procedure for the simultaneous determination of caffeine, theobromine, theophylline, catechin, and epicatechin in guarana seeds by HPLC-UV/Vis. The composition of the mobile phase was optimized using a mixture design, where an adequate chromatographic separation was obtained with 92.4% of an aqueous solution of acetic acid (0.1% v v^− 1), 5.2% methanol, and 2.4% isopropanol. A mixture design using water, acetone, and ethanol was used to optimize the composition of the extractor solution for ultrasound-assisted extraction. The best conditions for simultaneous extraction of the target compounds were 1.45, 0.45, and 0.1 mL of water, ethanol, and acetone, respectively. After defining the extractor solution, we applied a Doehlert matrix to study the instrumental conditions of the ultrasonic bath. Instrumental parameters were optimized at 35 °C, 30% and 10.5 min for temperature, power, and extraction time, respectively. The proposed procedure was validated and applied for analysis of guarana seeds samples dried by different techniques. Our results indicated that post-harvest management can significantly change the catechin and epicatechin contents in guarana samples.