Since the first resolution experiments using several related resolving compounds simultaneously, numerous effective enantiomer separations were described proving the importance of synergic interaction effect of chiral resolving agents on the enantiomer separation efficiency. However, the usage of chiral resolving agents with similar structures in a certain Dutch resolution experiment is inevitable, achiral component also can enhance the separation efficiency. Resolution of ibuprofen ((±)-2-(4-isobutyl-phenyl)-propionic acid, (IBU)) was investigated in this study using R-(+)-phenylethylamine (PEA) resolving agent at less than equivalent molar ratio. Although ibuprofen as a non-steroidal anti-inflammatory drug is used in its racemic form, it is still in focus of many researches. In a previous work, different conditions for diastereomeric salt formation and sample preparation methods were examined showing the feasibility of resolving IBU by supercritical fluid extraction. Both have deep effects on the achievable resolution efficiency (F), defined as F= eeextr·Yextr + eeraff ·Y raff, where ee and Y are the enantiomeric excess and the yield of the extract and raffinate enantiomeric mixtures of IBU, respectively. Optimal molar ratio of PEA/IBU was first determined on the efficiency of enantiomer separation (F). Benzylamine (BA) was added to the sample as achiral compound, and the ratio of BA/PEA was altered systemically (at constant base/acid ratio) to test the separation behaviour when achiral component is present. Unreacted, free enantiomers of IBU (S-(+)-IBU rich mixture) were extracted with supercritical carbon dioxide using a lab scale supercritical extraction unit at the previously determined optimal extraction parameters (150 bar and 33°C). Residual enaniomers (R-(-)-IBU rich mixture) were retrieved from the raffinate using liquid-liquid extraction after the supercritical fluid extraction. Enantiomeric excess was determined by a calibration from optical purity measurements.