RESUMEN
Research into the application of deep eutectic solvents (DESs) in capillary electrophoresis (CE) is still in its infancy. Even so, a controversy has already arisen over the "true role" of DESs in CE. This is because the DESs employed previously were all hydrophilic, and it is therefore reasonable to speculate that they may be virtually completely dissociated into its initial components (hydrogen-bond acceptor (HBA) and hydrogen-bond donor (HBD)) in aqueous CE buffers. Since there seems to be no essential difference in CE performance between adding a DES and adding its two constituents separately (HBA and HBD) in a running buffer, the significance of using DESs in these CE systems has not been clearly established. In this context, this study established the first DES-based CE system in which a DES really worked as a single entity. To achieve this goal a hydrophobic DES (HDES), (-)-menthol:octanoic acid, was employed to act as a pseudo-stationary phase (PSP) in electrokinetic chromatography (EKC) mode. We found that the HDES is capable of forming stable aggregates (micro-droplets) which can act as a PSP in the running buffer. The novel HDES-type PSP exhibited impressive selectivities toward several groups of analogues, homologues, and isomers via hydrophobic mechanism. It can be used either solely for direct EKC separation, or in combination with traditional PSPs (e.g., cyclodextrins). As a proof-of-concept study, we have demonstrated that the synergistic effect generated in an "HDES + Hydroxypropyl-γ-cyclodextrin" dual-PSP system allowed an excellent separation of a simulated complex mixture consisting of 13 aromatic acids.
Asunto(s)
Cromatografía , Disolventes Eutécticos Profundos , Cromatografía/métodos , Electroforesis Capilar/métodos , Hidrógeno , Interacciones Hidrofóbicas e HidrofílicasRESUMEN
In this short communication, we report the use of a second-generation macrolide antibiotic, gamithromycin (Gam), as a novel chiral selector for enantioseparation in capillary electrophoresis (CE). A preliminary analysis of the experiment results shows that Gam is especially suitable for the separation of chiral primary amines. Factors influencing enantioseparations were systematically investigated including the composition of the background electrolyte (BGE), concentration of Gam, the type and proportion of organic solvents, applied voltage, etc. In particular, N-Methylformamide (NMF) was successfully used as a non-aqueous solvent for Gam, and shown to be extremely effective for the separation of primaquine (PMQ) and 1-aminoindan (AMI) when used alone or mixed with other commonly used non-aqueous solvents (e.g. methanol). To our knowledge this was also the first application of NMF as a non-aqueous solvent for antibiotic chiral selectors in CE. The best separations were obtained with 100 mM Tris, 125 mM H3BO3 and 80 mM Gam in methanol/NMF (25:75) solvent for PMQ and AMI, or 80-100 mM Gam in methanol for the other model analytes. Among the analytes, the resolution (Rs) of amlodipine (AML) reached up to 15.65, which is to our knowledge the highest value ever reported in CE studies for this compound (except for using molecularly imprinted polymers technique).
Asunto(s)
Antibacterianos/química , Electroforesis Capilar , Macrólidos/química , Amlodipino/análisis , Electrólitos , Formamidas/química , Indanos/análisis , Metanol/química , Primaquina/análisis , Solventes/química , EstereoisomerismoRESUMEN
In this work, tetraalkylammonium amino acid ionic liquids (TAA-AAILs) were first applied to non-aqueous capillary electrophoresis (NACE) to establish synergistic systems with a conventional chiral selector, native ß-cyclodextrin (ß-CD). Excellent enantioseparations of some dansyl-amino acid (Dns-AA) samples were achieved. A series of comparison experiments and a molecular docking study were performed to validate the synergistic effect of TAA-AAILs and ß-CD in NACE. Several interesting results were observed compared with previously reported chiral ILs-related aqueous CE studies. In particular, the direct enantioselectivity of TAA-AAILs was observed for the first time by using it as sole chiral selector in NACE. This was an encouraging finding because it was the first direct and convincing evidence that AAILs were able to participate in the enantiorecognition process in the conventional chiral selectors-based synergistic systems. The new TAA-AAILs synergistic NACE system was further optimized in terms of alkyl chain length, TAA-AAILs concentration, ß-CD concentration, electrolyte composition and applied voltage, etc. Best enantioseparations of Dns-AAs were obtained when 100 mM ß-CD and 10 mM tetramethylammonium-l-arginine (TMA-l-Arg) were added in an NMF buffer containing 50 mM Tris and 35 mM CA (apparent pH 7.85) under UV detection. The applied voltage was set at 30 kV. The method was then successfully employed for the determination of enantiomeric impurities of a real AA sample. This work proved that the use of chiral ILs as additives in NACE is a promising approach for enantioseparation.
Asunto(s)
Electroforesis Capilar/métodos , Líquidos Iónicos/química , Arginina/análogos & derivados , Arginina/química , Tampones (Química) , Electrólitos/química , Concentración de Iones de Hidrógeno , Simulación del Acoplamiento Molecular , Compuestos de Amonio Cuaternario/química , Estereoisomerismo , beta-Ciclodextrinas/químicaRESUMEN
The application of chiral ionic liquids (ILs) in capillary electrophoresis (CE) for enantioseparation has received considerable attention in the past few years; however, the use of chiral ILs as ligands in ligand-exchange capillary electrophoresis (LE-CE) has been reported only in a few papers. In this work, several tetraalkylammonium amino acid ILs (TAA-AAILs) including tetramethylammonium-l-arginine (TMA-l-Arg), tetramethylammonium-l-proline (TMA-l-Pro) and tetramethylammonium-l-glutamic acid (TMA-l-Glu) were first applied in LE-CE to act as chiral ligands for enantioseparation. The results show that TMA-l-Arg-is an excellent chiral ligand, and able to yield equal or even better resolutions (Rs) in much shorter migration times for most tested analytes compared with previously reported AAILs ligands or free l-Arg-ligand. Parameters of the new TAA-AAILs-based LE-CE system such as the alkane chain length of TAA-AAILs, ILs configuration, ILs concentration, the type and concentration of central metal ion, buffer pH and applied voltage were optimized. Satisfactory enantioseparations were achieved for most selected free- or dansyl-amino acids. The method was then successfully applied to the enantiomeric impurity test of a commercial amino acid sample. This work indicates that the application of TAA-AAILs as chiral ligands in LE-CE is of great potential for enantioseparation.