Open tubular capillary column immobilized with sulfobutylether-β-cyclodextrin for chiral separation in capillary electrochromatography

Application of sodium sulfobutylether-β-cyclodextrin based on encapsulation

Sodium Sulfobutylether-β-cyclodextrin (SBE-β-CD) is a derivative of β-cyclodextrin, characterized by its stereo structure, which closely resembles a truncated cone with a hydrophobic internal cavity. The solubility of insoluble substances within the hydrophobic cavity is significantly enhanced, reducing contact between the guest and the environment. Consequently, SBE-β-CD is frequently employed as a co-solvent and stabilizer. As the research progresses, it has been observed that the inclusion of SBE-β-CD is reversible and competitive. Besides, some inclusion complexes undergo distinct physicochemical property alterations compared to the guests. Additionally, certain guests exhibit varying inclusions with SBE-β-CD at different concentrations. These features have contributed to the expanding applications. SBE-β-CD finds widespread application in pharmaceutics as a protective agent and pKa regulator, in pharmaceutical analysis as a chiral substance separator, and in biomedical engineering for encapsulating dyes and modifying sensors. The article will elaborate in detail on the physicochemical properties of SBE-β-CD, encapsulation principles, and factors influencing the formation of inclusion complexes. Furthermore, the review focuses on the application of SBE-β-CD through encapsulation in pharmaceutics, pharmaceutical analysis, and biomedical engineering. Finally, the prospects and potential applications of SBE-β-CD are discussed.

Recent developments in electromigration techniques related to pharmaceutical and biomedical analysis - A review

The analysis of pharmaceutical compounds is an important research topic as the use of different drugs affects people's daily life for the treatment of diseases. In addition to the widespread use of the internet, counterfeit drugs have appeared in the market. The development of modern analytical techniques, reliable, precise, sensitive, and rapid methods, has provided powerful means of analysis used in various fields such as drug production, quality control, determination of impurities and/or metabolites, biochemistry, pharmacokinetics, etc. Analytical techniques so far used in the pharmaceutical analysis include high-performance liquid chromatography (HPLC), gas chromatography (GC), super/sub-critical fluid chromatography (SFC), and capillary electromigration techniques such as capillary electrophoresis (CE) and rather rarely capillary electrochromatography (CEC). CE has some advantages over other techniques, e.g., very high efficiency, reduced costs (use of minute volumes of solvents and samples), the possibility to use different separation mechanisms, etc. In this review paper, the main features and limitations of the capillary electromigration techniques (especially CE) are discussed. Some selected applications of CE to the analysis of pharmaceutical compounds published in the period 2021-2023 (May) are reported.

Enantioseparation by zeolitic imidazolate framework-8-silica hybrid monolithic column with sulfobutylether-β-cyclodextrin as a chiral additive in capillary electrochromatography

A zeolitic imidazolate framework (ZIF)-8-silica hybrid monolithic column was prepared by one-step sol-gel method. The stationary phase in the monolithic column was characterized by Fourier-transform infrared spectra, X-ray diffraction, thermogravimetric analysis, nitrogen adsorption/desorption, and zeta potential. The results showed that ZIF-8-silica hybrid monolithic materials had abundant functional groups, good crystallinity, large specific surface area, and good thermal stability. A capillary electrochromatography (CEC) chiral separation system was for the first time constructed with ZIF-8-silica hybrid monolithic column and sulfobutylether-β-cyclodextrin (SBE-β-CD) as a chiral additive and was applied to separate the selected single and mixed chiral compounds (13 natural amino acids and 5 chiral pesticides). Under the optimized CEC conditions, all the single analytes achieved baseline separation with resolution of 2.14-5.94 and selectivity factor of 1.06-1.49 in less than 6 min, and the mixed amino acids with similar properties were also simultaneously enantioseparated (Rs ≥ 1.82). Relative standard deviations (RSDs) of migration time and column efficiency were lower than 4.26% and did not change significantly after 200 runs, evidencing excellent reproducibility and stability. These results demonstrate that the application of SBE-β-CD as a chiral additive for ZIF-8-silica hybrid monolithic columns is a promising method for the separation of chiral compounds.

Preparation of β-cyclodextrin covalent organic framework-immobilized poly(glycidyl methacrylate) nanoparticle-coated open tubular capillary electrochromatography column for chiral separation

A new enantioselective open-tubular capillary electrochromatography was developed employing poly(glycidyl methacrylate) nanoparticles/β-cyclodextrin covalent organic frameworks chemically immobilized on the inner wall of the capillary as a stationary phase. A pretreated silica-fused capillary reacted with 3-aminopropyl-trimethoxysilane followed by poly(glycidyl methacrylate) nanoparticles and β-cyclodextrin covalent organic frameworks through a ring-opening reaction. The resulting coating layer on the capillary was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The electroosmotic flow was studied to evaluate the variation of the immobilized columns. The chiral separation performance of the fabricated capillary columns was validated by the analysis of the four racemic proton pump inhibitors including lansoprazole, pantoprazole, tenatoprazole, and omeprazole. The influences of bonding concentration, bonding time, bonding temperature, buffer type and concentration, buffer pH, and applied voltage on the enantioseparation of four proton pump inhibitors were investigated. Good enantioseparation efficiencies were achieved for all enantiomers. In the optimum conditions, the enantiomers of four proton pump inhibitors were fully resolved within 10 min with high resolutions of 9.5-13.9. The column-to-column and inter- to intra-day repeatability of the fabricated capillary columns through relative standard deviation were found better than 9.54%, exhibiting satisfactory stability and repeatability of the fabricated capillary columns.

Lipase-based MIL-100(Fe) biocomposites as chiral stationary phase for high-efficiency capillary electrochromatographic enantioseparation

A novel chiral porous column was fabricated by lipase immobilized MIL-100(Fe) biocomposites as chiral stationary phase through covalent coupling and applied to capillary electrochromatographic enantioseparation. MOF-based lipase biocomposites not only enhance stereoselective activities but also improve the stability and applicability of the enzyme. The functionalized porous columns were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and powder X-ray diffraction. The performance of the porous column was evaluated by enantioseparating amino acid enantiomers, affording high resolution over 2.0. Besides, the enantio-resolutions of phenylephrine, phenylsuccinic acid, chloroquine, and zopiclone were also greater than 2.0. The relative standard deviations of run-to-run, intra-, and inter-day repeatability were within 4.0% in terms of resolution and retention time, exhibiting excellent stability of the column. Conceivably, the results show that MOF-based lipase composites as chiral stationary phase offer a highly efficient means for enantioseparation in capillary electrochromatography, attributing to the enhanced enantioselective activities of lipase by highly ordered frameworks.

Recent applications and chiral separation developments based on stationary phases in open tubular capillary electrochromatography (2019–2022)

Capillary electrochromatography (CEC) plays a significant role in chiral separation via the double separation principle, partition coefficient difference between the two phases, and electroosmotic flow-driven separation. Given the distinct properties of the inner wall stationary phase (SP), the separation ability of each SP differs from one another. Particularly, it provides large room for promising applications of open tubular capillary electrochromatography (OT-CEC). We divided the OT-CEC SPs developed over the past four years into six types: ionic liquids, nanoparticle materials, microporous materials, biomaterials, non-nanopolymers, and others, to mainly introduce their characteristics in chiral drug separation. There also added a few classic SPs that occurred within ten years as supplements to enrich the features of each SP. Additionally, we discuss their applications in metabolomics, food, cosmetics, environment, and biology as analytes in addition to chiral drugs. OT-CEC plays an increasingly significant role in chiral separation and may promote the development of capillary electrophoresis (CE) combined with other instruments in recent years, such as CE with mass spectrometry (CE/MS) and CE with ultraviolet light detector (CE/UV).

On the separation of enantiomers by drift tube ion mobility spectrometry

Racemic mixtures of twelve common α-amino acids and three chiral drugs were tested for the separation of their enantiomers by drift tube ion mobility spectrometry (IMS)-quadrupole mass spectrometry (QMS) by introducing chiral selectors into the buffer gas of the IMS instrument. (R)-α-(Trifluoromethyl)benzyl alcohol, (L)-ethyl lactate, methyl (S)-2-chloropropionate, and the R and S enantiomers of 2-butanol and 1-phenyl ethanol were evaluated as chiral selectors. Experimental conditions were varied during the tests, including buffer gas temperature, concentration and type of chiral selectors, analyte concentration, electrospray (ESI) voltage, ESI solvent pH, and buffer gas flow rate. The individual enantiomers yielded the same drift times and the racemic mixtures could not be separated. Energy calculations of the chiral selector-ion interactions showed that these separations are unlikely using 2-butanol as a chiral selector but they might be theoretically feasible depending on the chiral selector nature and the type of enantiomers. Several plausible explanations for not achieving separations were analyzed. Recommendations for potential enantiomer separations by IMS are proposed.