Peak distortion in reversed-phase liquid chromatography separation of active carbonyl-containing compounds: Mechanism...

Peak distortion is frequently encountered for compounds containing active carbonyl groups during reversed-phase (RP) LC separation. However, as being commonly overlooked or misdiagnosed, this problem is rarely reported in the literature and lacks an effective solution. In the present study, six pharmaceutical-related compounds containing keto or aldehyde groups, that exhibited severe peak distortion in early method development, were selected as the model compounds for further investigation. Systematic pH-screening experiments and a series of LC quadrupole-time of flight (Q-TOF) MS and NMR experiments were conducted on each model compound. The underlying chemical behavior of this type of compound during RP-LC separation was explicitly revealed. The formation of gem-diol/hemiketal/hemiacetal species via nucleophilic addition with H₂O/MeOH will occur in a low pH eluent, but will be completely suppressed when the pH is higher than an analyte-specific value. As further validated by twelve other pharmaceutical-related compounds belonging to this type, we confirmed that increasing the eluent pH using buffers without nucleophilicity is a simple and effective method to solve this peak distortion problem.