Supercritical fluid extraction of natural antioxidants from rosemary: Comparison with liquid solvent sonication

Supercritical fluid extraction (SFE) and liquid solvent sonication, in combination with two different sample treatments, were compared for the extraction of natural antioxidants from rosemary leaves. Dried, ground, and sieved rosemary leaves (20 mg) were subjected to SFE with CO2 at 355 bar at 100 degrees C (CO2 density 0.72 g/mL) for 20 min at a liquid now rate of 4 mL/min. The analytes were concentrated on an ODS trap and subsequently eluted with acetone, Antioxidants in the SF and liquid solvent extract were analyzed by HPLC, Compounds of known antioxidant activity such as carnosol, carnosic acid, and methyl carnosate were identified by mass spectrometry of the HPLC fractions collected, Freezing and grinding the samples in Liquid nitrogen resulted in decreased carnosic acid recoveries, Supercritical CO2 extraction provided the highest recovery of carnosic acid from rosemary leaves (35.7 mg/g), the lowest relative standard deviation (4.4%), and the cleanest extract-no cleanup prior to HPLC was required. Among the liquid solvents studies, only acetone provided comparable results (73% recovery relative to SC-CO2 extraction); however, it required decoloration with active carbon prior to HPLC analysis.