Micellar electrokinetic chromatography for the analysis of d-amygdalin and its epimer in apricot kernel

We have developed a simple, rapid and reproducible method for the determination of d-amygdalin and its epimer by using micellar electrokinetic chromatography (MEKC). Separation of d-amygdalin was performed in a 20 mM sodium borate buffer (pH 8.5) containing 300 mM sodium dodecyl sulfate using a bare fused-silica capillary. The eluates were monitored by the absorbance at 210 nm. The applied electric field was 278 V/cm, and the time needed for the separation of d-amygdalin did not exceed 6 min. The calibration curve for d-amygdalin showed excellent linearity in the concentration range of 5–500 μg/ml. The migration time and the corrected peak area show relative standard deviations (n=6) of 0.86% and 1.48%, respectively. The limit of detection (S/N=3) for d-amygdalin was 2 μg/ml. Under acidic and neutral conditions, amygdalin exists only as the d-form; however, under basic conditions, it shows both the d- and l-forms with a concentration ratio of 1:1.3 (d-amygdalin/l-amygdalin). Results of HPLC, UV–Vis spectrophotometry, and mass spectrometry reconfirmed the identification of d-amygdalin and its epimer. The number of theoretical plates of d-amygdalin is about 100 000 in MEKC, which is significantly higher than ∼8000 of HPLC. This method has been successfully applied to the determination of amygdalin epimers in various apricot kernel extracts and pharmaceutical products.