Table 1.
The obtained resolution values during mobile phase optimization
| Experiment No. | Mobile phase composition | Rs1a | Rs2a | Rs3a | Rs4a |
|---|---|---|---|---|---|
| 1 | Methanol–ethyl acetate (3.5:6.5, v/v) | 1.32 | 1.24 | 1.34 | 0.57 |
| 2 | Methanol–ethyl acetate (3.0:7.0, v/v) | 1.35 | 1.33 | 1.37 | 0.62 |
| 3 | Methanol–ethyl acetate (2.5:7.5, v/v) | 1.42 | 1.37 | 1.40 | 0.70 |
| 4 | Methanol–ethyl acetate (2.0:8.0, v/v) | 1.47 | 1.39 | 1.45 | 0.83 |
| 5 | Methanol–ethyl acetate–chloroform (2.0:8.0:1.0, v/v/v) | 1.49 | 1.51 | 1.13 | 0.75 |
| 6 | Methanol–ethyl acetate–chloroform (2.0:8.0:0.8, v/v/v) | 1.52 | 1.53 | 1.22 | 0.78 |
| 7 | Methanol–ethyl acetate–chloroform (2.0:8.0:0.5, v/v/v) | 1.53 | 1.54 | 1.27 | 0.89 |
| 8 | Methanol–ethyl acetate–chloroform (2.0:8.0:0.2, v/v/v) | 1.55 | 1.57 | 1.35 | 0.94 |
| 9 | Methanol–ethyl acetate– acetone (2.0:8.0:1.0, v/v/v) | 1.46 | 1.44 | 1.21 | 1.13 |
| 10 | Methanol–ethyl acetate– acetone (2.0:8.0:0.8, v/v/v) | 1.47 | 1.47 | 1.23 | 1.17 |
| 11 | Methanol–ethyl acetate– acetone (2.0:8.0:0.5, v/v/v) | 1.49 | 1.48 | 1.27 | 1.22 |
| 12 | Methanol–ethyl acetate– acetone (2.0:8.0:0.2, v/v/v) | 1.51 | 1.49 | 1.36 | 1.28 |
aRs1, Rs2, Rs3 and Rs4 are the obtained resolutions between NPZ impurity B & NPZ, NPZ & PHN, PHN & PHN impurity A and PHN impurity A & PHN impurity B, respectively