Separation and determination of corynoxine and corynoxine B using chiral ionic liquid and hydroxypropyl-β-cyclodextrin as additives by field-amplified sample stacking in capillary electrophoresis.

A sensitive, fast, and effective method, field-amplified sample stacking (FASS) in capillary electrophoresis, has been established for the separation and determination of corynoxine and corynoxine B. Hydroxypropyl-β-CD (HP-β-CD) and tetrabutylammonium-L-glutamic acid (TBA-L-Glu) were used as additives in the separation system. Electrokinetic injection was chosen to introduce sample from inlet at 10 kV for 50 s after a water plug (0.5 psi, 4 s) was injected to permit FASS. The running buffer (pH 6.1) was composed of 40 mM sodium dihydrogen phosphate solution, 130 mM HP-β-CD, and 10 mM TBA-L-Glu and the separation voltage was 20 kV. Under the optimum conditions, corynoxine and corynoxine B were successfully enriched and separated within 12 min and the sensitivity was improved approximately by 700-900 folds. Calibration curves were in a good linear relationship within the range of 62.5-5.00 × 10  ng/mL for both corynoxine and corynoxine B. The limits of detection (S/N = 3) and quantitation (S/N = 10) were 14.9, 45.2 ng/mL for corynoxine and 11.2, 34.5 ng/mL for corynoxine B, respectively. Finally, this method was successfully applied for the determination of corynoxine and corynoxine B in the stems with hooks of Uncaria rhynchophylla and its formulations.