Challenges with retention and recovery of impurities containing acidic moieties during analytical UHPLC method development and validation for gefapixant freebase

• Published in: Journal of pharmaceutical and biomedical analysis Vol. 237; p. 115772
• Main Authors: Halsey, Holst, Hall, Jackson, Huang, Chunli, Liu, Wenjun, Parganiha, Priya, Song, Siqing, Duran-Capece, Alicia, Fett, Joseph, Mathkar, Shilpa, Lohani, Sachin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.01.2024
• Subjects: Acidic impurity; Charged surface hybrid; Gefapixant freebase; Peak shifting; UHPLC method; Acidic impurity; UHPLC method; Charged surface hybrid; Gefapixant freebase; Peak shifting
• ISSN: 0731-7085; 1873-264X
• DOI: 10.1016/j.jpba.2023.115772

Gefapixant citrate is a P2X3 purinergic receptor antagonist developed for the treatment of chronic cough. Gefapixant freebase is the penultimate intermediate in the commercial manufacturing route for gefapixant citrate and contains a complex impurity profile consisting of acidic and basic analytes. A UHPLC method was developed for assay and purity determination of gefapixant freebase utilizing a Waters Acquity Charged Surface Hybrid (CSH) C18 column (2.1 mm I.D. x 10 cm length, 1.7 µm particle size) with 0.1 % phosphoric acid and acetonitrile as the mobile phases. Method optimization was performed using ACD Labs LC Simulator to achieve baseline separation of all impurities and the method was successfully validated. During routine use and method transfer for gefapixant freebase, an increase in retention time for impurities containing strongly acidic functional groups, and poor recovery of a sulfinic acid impurity were observed. Subsequent investigation determined that the CSH column aging resulting from exposure of the column packing to the acidic mobile phase was the root cause for these behaviors. The mechanism of peak-shifting was further investigated using model compounds and determined to be due to an increase in ionic interactions with the CSH stationary phase with routine column use. The increase in ionic interactions was demonstrated to correlate with the charge state of the analyte. Poor recovery for the sulfinic acid impurity was attributed to increased peak tailing for this single impurity on older columns. This knowledge was leveraged to establish additional system suitability requirements to monitor column performance for the lifecycle of the analytical procedure. •UHPLC method development and validation for gefapixant freebase.•ACD Labs LC Simulator for UHPLC method optimization.•Poor recovery for a sulfinic acidic impurity due to peak tailing on old columns.•Changes in selectivity for acidic impurities on CSH columns during routine use.•Impurity recovery and retention time requirements for column evaluation.