Liquid chromatographic separation of the stereoisomers of thiazide diuretics

A number of racemic thiazide diuretics and analogues were resolved on two diastereomeric chiral stationary phases (CSPs) prepared from (S)- or (R)-alpha-[1-(6,7-dimethyl)naphthyl]-10-dodecenylamine and (S)-2-phenylpropanoic acid. Of the two diastereomeric CSPs, the (S,S) and the (R,S), the former is found to be better than the latter in separating the enantiomers of the racemic thiazide diuretics and their analogues with complete separation being observed on the (S,S)-CSP. Chiral recognition is controlled principally by the (R)- or (S)-alpha-[1-(6,7-dimethyl)naphthyl]-10-dodecenylamine portion of the CSPs. The second stereogenic center of the CSP provides but secondary effects on the chiral recognition presumably involving, in the case of the (S,S)-CSP, face-to-edge pi-pi interaction between the aromatic ring of the analytes and the phenyl on the second stereogenic center.     

Liquid and gas chromatographic separation of isomeric methylated dibenzothiophenes

Trace amounts of a dibenzothiophene (DBT) series in complex matrices were detected by gas chromatography with flame photometric detection (FPD) after purification and isolation by normal-phase high performance liquid chromatography. The gas chromatographic behavior of eleven methylated DBTs was studied on six common stationary phases. Complete resolution of the four monomethyl DBT isomers was only achieved on a capillary column coated with a methylphenylsilicone phase gummified in situ by heat-curing. The determination of the relative distribution of the four monomethylated isomers is proposed as a powerful method for monitoring oil pollution in marine environment.     

Liquid chromatographic separation of fluoroquinolone antibacterials used as veterinary drugs

Summary A liquid chromatographic method has been developed to separate a series of quinolones which are widely used as veterinary drugs: danofloxacin, difloxacin, enrofloxacin (and its metabolite ciprofloxacin), marbofloxacin, norfloxacin and sarafloxacin. Separation was performed by using an end-capped high-purity silica-based C₈ column and a mobile phase consisting of acetonitrile-aqueous oxalic acid buffer solution. In order to establish the optimal conditions for an isocratic separation, a three-factor Doehlert experimental design was applied. Gradient elution was applied which reduced analysis time. Figures of merit of the method proposed, with fluorimetric detection, were evaluated.     

Liquid chromatographic separation and UV determination of certain antihypertensive agents

Three antihypertensive agents were extracted and isolated from commercial formulations. These were purified and characterized by melting point, lambdamax and IR. The percentage recovery by extraction process was in the range 81-91%. Active ingredients from binary formulations were separated by RP-HPLC using methanol-water (50:50 v/v) and by TLC using CHCl3-CH3OH (6:1) as mobile phase. Detection was by UV at 210 nm in HPLC, and by iodine vapors in TLC. The solvent conditions from TLC were transferred to open column chromatographic separation. Quantitative determination was carried out using TLC and column chromatography supplemented with UV spectrophotometry. Recovery was in the range 82-93%. Two combination of drugs, viz. amlodipine+ramipril and amlodipine+enalapril, were separated by the three modes of liquid chromatography. The percentage recovery was in the range 80-92% by open column.     

Liquid chromatographic separation of enantiomers using chiral additives in the mobile phase

Addition of an optically active compound to the mobile phase is an attractive method for resolving enantiomers in liquid chromatography. The technique is practical, easy to use and allows rapid screening for new chiral complexing agents as well as for optimal separation conditions.     

Analysis and chromatographic separation of some steroid hormones on NH2 layers

Summary The previously described analytical method for carbohydrates, catecholamines, uric acid, creatine and creatinine using thin-layer chromatography on aminomodified HPTLC plates and subsequent thermal activation of the chromatogram zones is expanded to include several steroid hormones. Specifically, they are the pharmacologically relevant compounds cortisone and hydrocortisone, estradiol and estradiol benzoate, estriol, estrone, methyltestosterone, testosterone and testosterone propionate, prednisolone, pregnandiol and triol, progesterone and Reichstein's S.     

Liquid chromatographic separation of electrochemical oxidation products of biologically important purines

A liquid Chromatographie method utilizing a dual column system (Sephadex G-10 gel permeation and Sephadex QAE A-25 anion exchange) has been developed for the quantitative separation of mixtures of compounds found as products of electrochemical oxidation of biologically important purines. Milligram quantities of such product mixtures may be separated and quantitative analysis is also possible in some cases.     

Liquid chromatographic separation of 2,4,6-trinitrotoluene and its principal reduction products

A liquid chromatographic method is described for the baseline separation of 2,4,6-trinitrotoluene (TNT) and its main reduction products. Two analytical columns (LC-18 and LC-CN) are connected in series and eluted isocratically at 1.5 ml min^?1 with water-methanol-tetrahydrofuran (60.5 + 25 + 14.5). The capacity factors (k′) are 1.4, 1.6, 5.1, 6.4 and 7.0 for 2,6-diamino-4-nitroluene, 2,4-diamino-6-nitrotoluene, TNT, 4-amino-2,6-dinitrotoluene and 2-amino-4,6-dinitrotoluene, respectively.     

Liquid chromatographic enantiomer separation with special focus on zwitterionic chiral ion-exchangers

This article provides a condensed introduction to principles of chiral separation, gives a historic overview of the genesis of the most important concepts regarding chiral stationary phase (CSPs), and summarizes the state of the art in a concise manner. Some recent developments in the field of polysaccharide CSPs are outlined. Finally, the article focusses on the new concept of zwitterionic chiral stationary phases and their application profile and peculiarities. Some other trends in column technology, including sub-2 μm and core–shell CSP particles and the emerging field of (UP)SFC, are briefly discussed. Figure

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Liquid chromatographic separation of metal ions on several silica-bound chelating-agent stationary phases

Summary The separation of metal-ions on several new silica-bound azo-coupled chelating stationary phases is described. Retention on 2-methyl-8-quinolinol and N-(1-naphthyl)-ethylenediamine phases is in the order of known homogeneous-solution stability constants. Very short retention times were obtained on the 2-methyl-8-quinolinol phase compared to an 8-quinolinol phase. A reversed order of retention was observed on -diketone and dithizone stationary phases in tartrate mobile phase. Two different mechanisms of metal-column interaction appear to occur. Large pH and mobile-phase buffer concentration effects were exhibited, especially by the diketone and dithizone phases. An excellent separation of a six-metal mixture is demonstrated on a dithizone column.     

Liquid chromatographic separation of phosphoramidate diastereomers on a polysaccharide-type chiral stationary phase

To improve the therapeutic potential of anti-HIV nucleoside analogues (d4T, AZT, 3TC and ddl), the delivery of the corresponding monophosphate from neutral, membrane-permeable prodrugs has been realised by the synthesis of lipophilic phosphoramidate triester prodrugs, such as the simple phenyl-L-alaninephosphate derivatives. However, the present non-stereoselective synthesis results in a mixture of 1:1 diastereomers, which differ from the configuration of the phosphorus atom asymmetric center. Since each diastereomer may have different biological activity and pharmacokinetic profile, analytical methods have to be developed for their separation. This work aims at showing the ability of a polysaccharide-type chiral stationary phase to resolve such diastereomers in reversed-phase high-performance liquid chromatography. The influence of operating parameters has been studied to optimise the separation; a thermodynamic approach has also been investigated to gain an insight in the retention mechanism of the prodrugs. Preliminary validation study (linearity, accuracy, repeatability) has yielded good results; in addition, the feasibility of HPLC-electrospray-mass spectrometry (HPLC-ESI-MS) coupling has been demonstrated and it is expected that this will lead to lower detection limits.     

Liquid chromatographic separation of terpenoid pigments in foods and food products.

The newest achievements in the use of various liquid chromatographic techniques such as adsorption and reversed-phase thin-layer chromatography and HPLC employed for the separation and quantitative determination of terpenoid-based color substances in foods and food products are reviewed. The techniques applied for the analysis of individual pigments and pigments classes are surveyed and critically evaluated. Future trends in the separation and identification of pigments in foods and food products are delineated.     

Liquid chromatographic separation of enantiomers of beta-amino acids using a chiral stationary phase

The enantiomers of both alpha-substituted beta-alanines and beta-substituted beta-alanines may be chromatographically separated using silica-bonded chiral stationary phases derived from N-acetylated alpha-arylalkylamines. The amino acids are chromatographed as alkyl esters of N-3,5-dinitrobenzoyl derivatives; separability factors range from 1.11 to 1.65 for nine alpha-substituted beta-alanines and from 1.08 to 1.20 for nine beta-substituted beta-alanines. The enantiomers of beta-aminoisobutyrate and beta-leucine, chiral beta-amino acids occurring in animal tissues and physiological fluids, are among those resolved. The enantiomers of R,S-beta-aminoisobutyrate and several related alpha-alkyl-beta-alanines were prepared by chromatographic resolution of diastereomeric dipeptides.     

Liquid chromatographic enantiomer separation of racemic amine using chiral crown ether stationary phase

Direct enantioseparation of racemic amine, amino-thiophene-2-yl-acetonitrile (TAN), on chiral crown ether stationary phase [Crownpak CR (+)] is described in this study. The elution behavior and the effect of acid additives on resolution of racemic amine, TAN, is intensely investigated. Moreover, the chiral recognition mechanism in this specific system is proposed based on computational methods with the density functional theory. Diastereomeric complexation of the ammonium ion of racemic amine inside the cavity of chiral crown ether appears essential for the chiral discrimination. The pH of the mobile phase containing acid additives also acts as an important factor for the chiral recognition.     

Liquid chromatographic separation of alkaloids in herbal medicines: Current status and perspectives

Alkaloids are a widespread group of basic compounds in herbal medicines and have attracted great interest due to various pharmaceutical activities and desirable druggability. Their distinctive structures make chromatographic separation fairly difficult. Peak tailing, poor resolution, and inferior column‐to‐column reproducibility are common obstacles to overcome. In order to provide a valuable reference, the methodologies and/or strategies on liquid chromatographic separation of alkaloids in herbal medicines proposed from 2012 to 2019 are thoroughly summarized.     

Liquid chromatographic separation of the enantiomers of beta-amino acids on a ligand exchange chiral stationary phase

A liquid chromatographic ligand exchange chiral stationary phase (CSP) derived from (S)-leucinol was applied in the separation of the enantiomers of 12 beta-amino acids. The resolution was quite successful especially for the enantiomers of beta-amino acids containing aromatic functional group in the side chain. The chromatographic resolution behaviors were dependent on the organic modifier and Cu(II) concentration in aqueous mobile phase and the column temperature.