Phosphoric acid

The standards of the compounds analyzed by liquid chromatography (chlorogenic acid, caffeine, and rutin) were provided by Sigma Aldrich (St. Louis, MO, USA). HPLC-grade acetonitrile and mEthanol were supplied by the company Merck (São Paulo, Brazil). The ultra-pure water was provided by a Purelab Flex 3 purifying system (Elga Veolia, High Wycombe, United Kingdom). Ethanol (99.5%), phosphoric acid (85%), hydrochloric acid, and sodium hydroxide were purchased from Labsynth (São Paulo, Brazil). The adsorbents used in this study were: Sepra C18-E, (particle size: 50 μm, pore size: 85 Å, Phenomenex, Torrance, CA, USA); Isolute C18-EC, (particle size: 50 μm, poresize: 60 Å, Biotage, Sweden) and Strata X C18 (particle size: 33 μm, pore size: 85 Å, Phenomenex, Torrance, CA, USA).Yerba mate leaves were acquired in a local supermarket and stored at −20 °C until used as a sample. The particle size of the sample used for the experiments was between 1.41 and 2.00 mm.

Organic beetroot (Beta vulgaris L.) stalks and leaves, grown in May and April 2016, were obtained from a producer in the city of Limeira, São Paulo state, Brazil. All reagents used for analysis were of analytical grade. High-performance liquid chromatography (HPLC)-grade acetonitrile was obtained from J.T. Baker (Phillipsburg, NJ, USA), and phosphoric acid was obtained from Labsynth (Diadema, SP, Brazil). Vitexin-2-rhamnoside standard was purchased from Sigma-Aldrich (São Paulo, Brazil).