Isolation of carsonic acid from rosemary extracts using semi-preparative supercritical fluid chromatography

Supercritical fluid chromatography (SFC) in analytical and semi-preparative scale was studied to separate rosemary (Rosmarinus officinalis) supercritical extracts to produce fractions with high antioxidant activity. Carnosic acid, the major antioxidant present in rosemary supercritical extracts, was the target compound to be isolated in the fractions produced. First, rosemary extracts were produced in a supercritical CO2 pilot-plant employing different extraction conditions, in order to obtain samples with diverse composition. The content of carnosic acid was determined and the DPPH test was accomplished in order to assess the antioxidant activity of the different samples produced. Then, using some of these samples, experiments were carried out in a semi-preparative SFC system testing the performance of four different chromatographic columns to isolate and recover a fraction with high concentration of carnosic acid. The four chromatographic columns employed were silica and 2-ethylpyridine (especially packed for SFC) and silica and diol columns (packed for HPLC). The SFC fractionation conditions explored were in the ranges 10–20 MPa, 313–333 K and 5–20% of cosolvent (ethanol). Using the first three columns, it was possible to isolate fractions with concentrations of carnosic acid greater than 80% mass.

► Several rosemary extracts with different compositions were obtained by SFE.
► SFC was used to isolate the main antioxidant compound, namely carnosic acid.
► The 2-ethylpyridine column (10 MPa, 313 K and 20% ethanol) produced the best results.
► Carnosic acid purity close to 100% and high recovery (97%) was attained.