In addition, the impurities were detected by a gradient
reverse-phase high performance liquid chromatography (RP-HPLC) with UV detection. The
chromatographic system consisted of an Angilent Zobax SB-CN column (250 4.6 mm;
5 mm). The mobile phase consisted of water/acetonitrile/trifluoroacetic acid 1900:100:1 v/v/
v (solution A) and acetonitrile/water/trifluoroacetic acid 1900:100:1 v/v/v (solution B) using
a gradient program at a flow rate of 1.0 ml/min with 278 nm detection and an injection
volume of 20 ml.