Study of the changes in mono-, di- and trifunctional octadecyl-modified packings for reversed-phase high-performance liquid chromatography with different eluent compositions

Zeolite-based chiral ion-exchangers for chromatographic enantioseparations and potential applications in membrane separation processes

Chiral resolution of racemic compounds represents an important task in research and development and, most importantly, in the large-scale production of pharmaceuticals. Zeolites, which are already frequently utilized for their unique properties, represent materials that can be used for the development of new chiral stationary phases for liquid chromatography, simulated moving bed or enantioselective membranes. The aim of this study was to modify a series of MWW zeolites by a chiral anion-exchange type selector thereby creating a chiral stationary phase for enantiomeric resolution of acidic compounds. To evaluate the applicability of the prepared chiral stationary phase in liquid chromatography, we used N-protected amino acids as model analytes. First, we tested the new sorbents preferential sorption using N-(3,5-dinitrobenzoyl)leucine. We observed outstanding sorption properties of a zeolite-based sorbent (MCM-36), which were comparable to spherical chromatographic silica. This particular material was subsequently packed into a chromatographic column, which was tested under polar organic mode HPLC conditions facilitating baseline resolution of 5 out of 8 N-protected amino acids. Although the chromatographic performance shows several drawbacks (high backpressure, low column efficiency), it clearly documents the potential of the novel materials in chiral separation. To the best of our knowledge, this is the first example of the preparation of the chiral stationary phase based on MWW zeolites ever.

Daily validation procedure of chromatographic assay using gaussoexponential modelling

High performance liquid chromatography is one of the most successful analytical methods used for the quantitative determination of drugs in biological samples. However, this method is marked by a lack of performance reproducibility: chromatographic peaks become wider and even asymmetrical as the column ages. These progressive changes in the chromatographic parameters have to be taken into account when evaluating the validation criteria for the method. These criteria change with the ageing process of the column leading to the need for new estimations to assure the quality of the results. Procedures are proposed for the daily determination of some validation criteria using the exponentially modified Gaussian (EMG) model of the chromatographic peak. This modelling has been studied on simulated chromatographic peaks in order to obtain the relationships between chromatographic measurements and EMG parameters.