Table 2.
Experimental factors and settings for the multivariate designs of experiments.
| Design | Qualitative factor | Settings | |
|---|---|---|---|
| D-optimal design | pH of mobile phase | pH 2.8; pH 6.7 | |
| Organic solvent | Methanol; Acetonitrile | ||
| Type of gradient slopea | 4; 6; 8 | ||
| Quantitative factor | Lower limit | Upper limit | |
| Capillary voltage (kV) | 0.5 | 3.5 | |
| Gradient steepness (min) | 1.5 | 3.5 | |
| Flow rate (mL/min) | 0.4 | 0.6 | |
| CCF-design | Capillary voltage (kV) | 0.4 | 2.0 |
| Cone voltage (V) | 20 | 35 | |
| Flow rate (mL/min) | 0.35 | 0.45 | |
CCF, central composite face design.
a
Slope 4 is concave downwards; slope 6 is linear; slope 8 is concave upwards.