| Amount added | Glycopyrrolate | Methylparaben | Propylparaben |
| % Recovery | % Recovery | % Recovery | |
| 30 % | 100.1 | 100.2 | 100.2 |
| 100 % | 99.8 | 101.0 | 100.0 |
| 150 % | 98.9 | 100.8 | 100.8 |