| H+ (mol∙L−1) | Separation factor (FS) Zr/Hf | ||
| TBP | CYANEX®923 | TBP/CYANEX®923 | |
| 1.0 | 0.3 | 2.9 | 2.5 |
| 2.0 | 4.9 | 4.9 | 4.2 |
| 3.0 | 4.2 | 3.2 | 5.9 |
| 4.0 | 5.8 | 5.7 | 14.9 |
| 5.0 | 7.0 | 25.7 | 23.0 |
| 7.0 | 10.5 | 25.1 | 25.1 |
| 10 | 21.4 | 31.6 | 25.7 |