The HPLC apparatus consisted of a Dionex P580 LPG pump, an ASI-100 T autosampler, an STH 585 column oven, a PDA-100 UV detector or a Jasco (Tokyo, Japan) Model CD 2095 Plus UV/CD detector; data were acquired and processed by a Chromeleon Datasystem (Dionex Corporation, Sunnyvale, CA). For semipreparative separation, a Perkin-Elmer (Norwalk, CT, USA) 200 LC pump equipped with a Rheodyne (Cotati, CA, USA) injector, a 5000 μL sample loop, a Perkin-Elmer LC 101 oven and Waters 484 detector (Waters Corporation, Milford, MA, USA) was used. The signal was acquired and processed by Clarity software (DataApex, Prague, The Czech Republic).
In analytical separations, fresh standard solution of OME and single impurities were prepared shortly before using by dissolving 1–3 mg of each analyte in the mobile phase.
In order to ensure reproducible chromatographic performance, after the incorporation of acid or basic additives into the mobile phase, the IG-3 column was washed with the following mobile phases: ethanol at 0.5 mL/min for 30 min, followed by tetrahydrofuran at 0.5 mL/min for 120 min and, finally, ethanol at 0.05 mL/min for 120 min.
In analytical separations, fresh standard solution of OME and single impurities were prepared shortly before using by dissolving 1–3 mg of each analyte in the mobile phase.
In order to ensure reproducible chromatographic performance, after the incorporation of acid or basic additives into the mobile phase, the IG-3 column was washed with the following mobile phases: ethanol at 0.5 mL/min for 30 min, followed by tetrahydrofuran at 0.5 mL/min for 120 min and, finally, ethanol at 0.05 mL/min for 120 min.