Simultaneous quantitative determination of major phenolics in rosemary extract via DPPH reagent free-radical-scavenging activity.

Rosemary extracts are convenient sources of natural antioxidants particularly phenolic constituents. This group is mainly constituted by several minor flavonoids, while the main components are rosmarinic acid and the diterpenoid compound known as carnosic acid. Consequently the quality of commercial extracts depends on the claimed antioxidant content calculated as rosmarinic acid (RA) and carnosic acid (CA). Therefore a rapid and selective method aiming to evaluate the above mentioned features should be highly desirable. A HPTLC-densitometric method, based on external standard approach combined with DPPH radical in situ derivatization, was developed for routine analysis of RA and CA in rosemary extracts. This latter compound is reported to rapidly degrade toward the oxidized form of carnosol quinone in water media and carnosol in methanol. Therefore the problem of the chemical stability of the carnosic acid during the HPTLC analysis has been weighed up.