Hydrophilic interaction liquid chromatography method development and validation for the assay of HEPES zwitterionic buffer

Recent applications of retention modelling in liquid chromatography

Recent applications of retention modelling in liquid chromatography (2015–2020) are comprehensively reviewed. The fundamentals of the field, which date back much longer, are summarized. Retention modeling is used in retention‐mechanism studies, for determining physical parameters, such as lipophilicity, and for various more‐practical purposes, including method development and optimization, method transfer, and stationary‐phase characterization and comparison. The review focusses on the effects of mobile‐phase composition on retention, but other variables and novel models to describe their effects are also considered. The five most‐common models are addressed in detail, i.e. the log‐linear (linear‐solvent‐strength) model, the quadratic model, the log–log (adsorption) model, the mixed‐mode model, and the Neue–Kuss model. Isocratic and gradient‐elution methods are considered for determining model parameters and the evaluation and validation of fitted models is discussed. Strategies in which retention models are applied for developing and optimizing one‐ and two‐dimensional liquid chromatographic separations are discussed. The review culminates in some overall conclusions and several concrete recommendations.

Zwitterionic-hydrophilic interaction liquid chromatography for l-ascorbic acid 2-phosphate magnesium, a raw material in cell therapy

l-ascorbic acid 2-phosphate magnesium (APMg) salt is a vitamin C derivative frequently used in cell culture media for research purposes. It is also used as a raw material in the GMP-manufacturing of gene-, cell- and tissue advanced therapy medicinal products (ATMPs). However, quality methods are currently lacking. Therefore, a LC method was developed, based on hydrophilic interaction (HILIC)-ion exchange (IE) mixed-mode liquid chromatography. The final method consisted of an isocratic system with 15 mM KH₂PO₄ buffer (pH 2.5 with HCl) acetonitrile (30:70, v/v) mobile phase on a zwitterionic HILIC column, containing an hydrophilic ligand embedded cation-exchange functionality and a surface anion-exchange group. A flow rate of 0.4 mL/min and UV detection at 240 nm was applied. The assay method of APMg was validated, obtaining adequate linearity (R² = 0.999), precision (RSD of 0.49%) and accuracy (overall recovery of 100.4%). The developed method was successfully applied on five currently marketed products from different suppliers, showing different related substance impurity profiles. Using atomic absorption spectroscopy (AAS), magnesium was found to be bound on the stationary phase, requiring a strong mobile phase to rinse the column. Finally, related impurities were identified using MS/MS and high resolution MS, and found to be ascorbic acid as well as ethyl derivatives, which was further confirmed by NMR.