Enantioselective LC analysis of synephrine in natural products on a protein-based chiral stationary phase

An enantioselective LC method with photodiode array detection (PAD) was developed for the enantioseparation of (±)-synephrine from C. aurantium L. var. amara fruits and phytotherapic derivatives by using a protein-based chiral stationary phase with cellobiohydrolase as the chiral selector (Chiral-CBH). Analyses were carried out on a Chiral-CBH column (100 × 4.0 mm i.d., 5 μm), with a mobile phase consisting of 2-propanol (5%, w/w) in sodium phosphate buffer (pH 6.0; 10 mM) and disodium EDTA (50 μM). The flow rate was 0.8 mL/min. Detection was set at 225 nm. To identify the order of elution, the racemate was resolved by the preparation of suitable diastereoisomeric salts with antipodes of appropriate organic acids.

Isolation of synephrine from C. aurantium fruits and phytoproducts was performed by solid-phase extraction (SPE) with a strong cation-exchange phase.

The method developed was validated and was found to be linear in the 0.40–40.14 μg/mL range (r² = 1.000, P < 0.0001) for both synephrine enantiomers. The limit of detection (LOD) for each enantiomer was 0.04 μg/mL. The limit of quantification (LOQ) for each enantiomer was 0.13 μg/mL. Intra-day precision (calculated as %R.S.D.) ranged from 0.03 to 0.24% for (−)-synephrine and from 0.03 to 0.35% for (+)-synephrine. Inter-day precision (calculated as %R.S.D.) ranged from 0.07 to 1.45% for (−)-synephrine and from 0.06 to 1.26% for (+)-synephrine. Intra- and inter-day accuracies (calculated as %recovery) were in the ranges of 97.4–100.6 and 98.0–101.6% for (−)-synephrine, and in the ranges 97.0–101.5 and 98.1–102.8% for (+)-synephrine.

The results of the application of the method to the analysis of C. aurantium samples showed that (−)-synephrine was the main component. (+)-Synephrine was not detected in C. aurantium fruits and was present in low concentration in the phytoproducts.