Separation of β-blocker and amino acid enantiomers on a mixed chiral sorbent modified with macrocyclic antibiotics eremomycin and vancomycin

A mixed chiral sorbent based on silica with immobilized macrocyclic antibiotics eremomycin and vancomycin was synthesized. A possibility of the separation of enantiomers of β-blockers (metoprolol, pindolol, alprenolol, oxprenolol, labetalol, and atenolol) and amino acids (tryptophan, phenylalanine, DOPA, methionine, and acetyl glutamic acid) on this chiral sorbent by HPLC was studied. The influence of the composition of the mobile phase (pH of buffer solution, its concentration, content of organic modifier, and its nature) on the retention times of β-blocker and amino acid enantiomers, selectivity, and resolution of peaks was studied. It was shown that the mixed chiral sorbent has enantioselectivity to both classes of compounds, while silica modified with vancomycin has no ability to the separation of enantiomers of non-derivatized amino acids, and silica modified with eremomycin has no ability to the separation of β-blocker enantiomers. High values of resolution for amino acids (max Rs > 4) and β-blockers (max Rs > 1) were obtained.     

Thin Layer Chromatographic Study of Bauxite and Quantitative Estimation of Co-Existing Al3+, Fe2+ and Ti4

 Thin layer chromatography in combination with spectrophotometry and titrimetry has been used to evaluate chromatographic characteristics of bauxite constituents. The retention behaviors of four major constituents (Al3+, Fe2+, Ti4+, Si4+) in bauxite mineral have been examined on plain and modified layers of silica gel G, silica gel H and cellulose with mobile phases containing aqueous sodium chloride, formic acid and hydrochloric acid. Ternary separation of Al-Fe-Ti was achieved on chromatographic plates made of silica gel H. The pH effect and presence of impurity elements in samples, nature of stationary phases on the ternary separation and detection limits of bauxite constituents were studied. Silicon in bauxite was detected on cellulose plates. Quantitative determinations of Al3+, Fe2+ and Ti4+ on silica gel H impregnated with sodium formate layers were achieved by titrimetry and spectrophotometry.     

Analysis of conjugated bile acids by packed-column supercritical fluid chromatography.

A rapid method has been developed for the simultaneous separation of the polar glycine- and taurine-conjugated bile acids by packed-column supercritical fluid chromatography. Samples were analysed on a cyanopropyl-bonded silica column with ultraviolet detection at 210 nm and carbon dioxide modified with methanol as the mobile phase. The influence of the stationary phase, modifier concentration, temperature, column pressure and modifier identity on retention was also studied. This new chromatographic method is applicable to the assay of conjugated bile acids in duodenal bile samples from patients with hepatobiliary diseases.     

In-situ carbonizing of coal pitch on the surface of silica sphere as quasi-graphitized carbon stationary phase for liquid chromatography

A novel chromatography stationary phase with a quasi-graphitized carbon modified shell has been developed. Coal pitch was directly carbonized on the surface of porous silica with in-situ carbonization. The carbonized coal pitch coating exhibits some degree of graphitization with a 78 nm-thick layer on the surface of silica and a 0.5 nm-thick layer on the inner surface of the mesopores. Based on the special structure of the graphitized carbon coating, the novel stationary phase can provide multiple interactions such as hydrophobic interaction, π-π interaction and dipole-dipole interaction. The novel composite material exhibited unique separation selectivity and excellent separation efficiency for polar compounds, including imidazoles, nucleosides and pesticides. Besides, the packed column also exhibited great repeatability with the RSDs of the retention time of nucleosides between 0.07%-0.50% (n = 5). Finally, satisfied result was achieved in the separation of fullerenes on the new column, suggesting the great potential in the industrial-scale purification of fullerenes.     

氯甲基苯乙烯包夹硅基单柱强阴离子色谱柱的研究

采用氯甲基苯乙烯包夹硅胶基质制备出一种新型强阴离子色谱柱填料，该填料具有良好的色谱柱性能，可以较地的分离常见的６种无机阴离子，６种低碳链有机酸以及甲酸，乙酸和一些无机阴离子的混合物。     

High performance liquid chromatography of aromatic carboxylic acids on p-tert-butyl-calix[8]arene-bonded silica gel stationary phase

A new p-tert-butyl-calix[8]arene-bonded silica gel stationary phase (CABS) was used for the separation of some aromatic carboxylic acids by HPLC. The chromatographic behaviour of the solutes on CABS was studied in comparison with conventional ODS. The results show that the calix[8]arene-bonded phase exhibits a stronger retention and better selectivity than ODS for the aromatic carboxylic acids. The different elution order of the analytes was also observed on both packings, which show the existence of distinct retention mechanisms. According to chromatographic data, it can be concluded that the high selectivity of CABS for aromatic carboxylic acids ascribes to various interactions between CABS and the analytes, such as hydrophobic interaction, hydrogen bonding interaction, π-π interaction and inclusion interaction.     

Reversed-phase systems for the separation of pentapeptides by high-performance liquid chromatography

Summary Reversed-phase systems using octyl modified silica as such and as a support for dynamically coated ion-exchangers, were investigated for their ability to separate pentapeptides. Normal reversed-phase adsorption with C-8 bonded silica in combination with citrate bufferpropanol-1 mixtures were found useful for the separation of a number of pentapeptides. The separation of pentapeptides differing widely in retention can be speeded up by applying an organic modifier and/or sodium citrate gradient. A solvent generated cation-exchange system with sodium dodecylsulfate as surfactant showed a high selectivity for the pentapeptides under investigation and is better for analytical purposes than the normal reversed-phase adsorption systems investigated. With respect to the detection of pentapeptides with fluorescamine, the use of dry pyridine as a basic buffer and as diluent for the fluorescamine was also investigated. Compared to the commonly used diluent acetone, pyridine is better when using acidic eluents of moderate buffer strength. At pH>6 no significant differences in sensitivity between acetone and pyridine could be noticed.     

Single-Run Separation and Determination of Aliphatic and Aromatic Carboxylic Acids in Wine and Human Urine Samples by Ion-Exclusion Chromatography

This work is focused on developing a new chromatographic method with UV detection for the separation and determination of thirty-two carboxylic aliphatic and/or aromatic acids in a single run. Ion-exclusion chromatography with a silica based, modified with C18, analytical column Alltech Prevail? organic acid 5 µm (150 mm × 4.6 mm I.D) was used for the solving of this problem. The developed method was based on ion-exclusion and/or hydrophobic interaction chromatographic separation mechanism. The effect of the concentrations of phosphate buffer and its pH as well as the column temperatures on the retention of the test acids has been investigated. Gradient elution of the mobile phase composed of aqueous phosphate buffer and methanol was used to achieve a required separation of carboxylic acids within 45 min. All measurements were done at 220 nm. Column temperature was set at 25 ± 0.1 °C. The LOD values for organic acids range from 0.002–2.224 mg L^?1. The repeatability of the procedure developed is characterized by the RSD, which varied between 0.52 and 2.85 % for the peak area. The proposed method was successfully applied for the determination of aliphatic and aromatic acids in dry white wine and human urine samples.     

High performance liquid chromatography with cyclodextrin and calixarene macrocycle bonded silica stationary phases for separation of steroids

β-Cyclodextrin, p-tert-butyl-calix[8]arene and chloropropyl bonded silica stationary phases have been prepared and were applied at the same time to develop a chromatographic procedure to separate steroids. In order to select the best type of stationary phase for the analysis, similar preparation processes of the two kinds of macrocycle stationary phases with the same spacer were adopted respectively. The chromatographic behaviors and retention mechanisms of the two kinds of macrocycle stationary phases for steroids were systematically studied and compared with those of chloropropyl bonded silica and ODS. The effect of mobile phase variables, such as methanol content, pH value of buffer, ionic strength and buffer composition on chromatographic behaviors was investigated. The results showed that the retention mechanisms of the four stationary phases for steroids were obviously different, and excellent separation was achieved on β-cyclodextrin bonded silica stationary phase (β-CD-BS), as a consequence of the structure and the properties of the stationary phase. The retention process on β-CD-BS exhibited inclusion complexation, hydrogen-bonding and weak hydrophobic interaction, while for p-tert-butyl-calix[8]arene bonded silica stationary phase (CBS), π-π and hydrogen-bonding besides hydrophobic interaction played an important role.     

High performance liquid chromatographic studies on lanthanides, uranium and thorium on amide modified reversed phase supports

The retention behavior of uranium, thorium and lanthanides has been investigated with amide modified reversed phase C₁₈ supports using α-hydroxy isobutyric acid (α-HIBA) as the mobile phase. Four structurally different amide moieties namely, 4-hydroxy-N,N-dihexyl butyramide (4HHBA), 4-hydroxy-N,N-di-2-ethylhexylhexanamide (4HEHHA), bis(N,N,N′,N′-2-ethylhexyl)malonamide (B2EHM) and N-methyl-tris(dihexylcarbamoyl-3-methoxy)pivolamide (MTDCMPA) have been synthesized and studied. Among the various amide coated columns, the supports modified with 4HHBA, B2EHM and MTDCMPA exhibit an interesting retention for uranium and thorium, which is different from 4HEHHA modified support. The retention time for uranium and thorium increases with increasing amide concentration for 4HHBA, B2EHM and MTDCMPA supports, while the same decreases with increasing 4HEHHA content. However, the separation factor for uranium and thorium is greater on a 4HEHHA support, compared to an unmodified C₁₈ column, reflecting the amide's preferential complexation of uranium over thorium.Columns modified with 4HHBA, B2EHM and MTDCMPA exhibit relatively higher retentions for lanthanides. However, MTDCMPA modified support shows a different elution profile for lanthanides compared to 4HHBA, and B2EHM modified columns. Individual separations of heavier lanthanides, i.e., from gadolinium to lutetium also have been achieved using 4HHBA and B2EHM modified supports.The influence of modifier content, mobile phase concentration and its pH on the retention of metal ions has also been studied. Based on these investigations, an efficient high performance liquid chromatographic method (HPLC) has been developed for the rapid separation of uranium from thorium as well as for the individual separation of heavier lanthanides.     

Properties of microdispersed sintered nanodiamonds as a stationary phase for normal-phase high performance liquid chromatography

The chromatographic properties of microdispersed sintered nanodiamonds (MSND) are studied under conditions of normal-phase HPLC. The retention characteristics of 30 substances representing four classes of aromatic compounds including monoalkylbenzenes, polymethylbenzenes, di-n-alkyl phthalates and polyaromatic hydrocarbons in n-alkane mobile phases have been measured. The selectivity of MSND was compared with literature data for other common adsorbents including silica gel, alumina and porous graphitic carbon (PGC). MSND shows the distinctive adsorption properties especially in a stronger retention of aromatic hydrocarbons and in the better selectivity of the separation of geometric isomers. The significant improvement in separation efficiency up to 45,300 theoretical plates per meter, was achieved for the first time for the columns packed with diamond related materials (DRM).     

Investigation of Symphytum cordatum alkaloids by liquid-liquid partitioning, thin-layer chromatography and liquid chromatography-ion-trap mass spectrometry

From the alkalised crude extract of Symphytum cordatum (L.) W.K. roots, pyrrolizidine alkaloids (PAs) were extracted as free tertiary bases and polar N-oxides in a merely one-step liquid-liquid partitioning (LLP) in separation funnel and subsequently pre-fractionated by preparative multiple-development (MD) thin-layer chromatography (TLC) on silica gel plates. In this way three alkaloid fractions of different polarities and retention on silica gel plates were obtained as: the most polar N-oxides of the highest retention, the tertiary bases of medium retention, and diesterified N-oxides of the lowest retention. The former fraction was reduced into free bases by sodium hydrosulfite and purified by LLP on Extrelut-NT3 cartridge. It was further analysed together with the two other fractions by high-performance liquid chromatography (HPLC)-ion-trap mass spectrometry with atmospheric pressure chemical ionization (APCI) interface on XTerra C₁₈ column using a gradient elution. Based on MSⁿ spectra, 18 various alkaloids have been tentatively determined for the first time in this plant as the following types of structure: echimidine-N-oxide (three diasteroisomers), 7-sarracinyl-9-viridiflorylretronecine (two diasteroisomers), echimidine (two diasteroisomers), lycopsamine (two diasteroisomers), dihydroechinatine-N-oxide, dihydroheliospathuline-N-oxide, lycopsamine-N-oxide (three diasteroisomers), 7-acetyllycopsamine-N-oxide, symphytine-N-oxide (two diasteroisomers) and 2″,3″-epoxyechiumine-N-oxide.     

Optimization of a high-performance liquid chromatography method for the analysis of complex polyphenol mixtures and application for sainfoin extracts (Onobrychis viciifolia)

A pentafluorophenylpropyl (PFP) stationary phase was tested for the simultaneous determination of several classes of phenolic compounds. The chromatographic results were compared with those obtained by using a bifunctional phase constituted of octadecyl and phenylpropyl bonded silica and three conventional C18 columns. The elution gradient was optimized with 5% formic acid and sodium acetate in combination with acetic acid as additives and methanol as solvents. For these evaluations, a complex phenolic extract of Onobrychis viciifolia (sainfoin) and test mixtures containing 54 standard substances including 2 simple phenolic compounds, 1 amino acid, 4 hydroxybenzoic acids (HBA), 6 hydroxycinnamic acids (HCA), 3 flavan-3-ols, 9 anthocyanins, 2 dihydroflavonols, 1 chalcone, 4 flavones, 1 isoflavone and 21 flavonols have been assayed. The perfluorinated column showed good resolution for the studied phenolic compounds which have the following elution order: HBA, HCA, flavan-3-ols, anthocyanins, dihydroflavonols, flavones, flavonols and isoflavones. Compared with other columns, it provides longer elution ranges for HBA, HCA and flavan-3-ols and increased retention times for all compound classes except anthocyanins which were similarly retained on a C18 column. Its selectivity is different from C18 and bifunctional phases. A high-performance liquid chromatography (HPLC) method with diode array detection (DAD) and post-column derivatization with p-dimethyl-aminocinnamic aldehyde (DMACA) has been validated for the analysis of individual phenolic compounds from a sainfoin plant extract (O. viciifolia).     

Effect of chromatographic conditions on the separation and system efficiency for HPLC of selected alkaloids on different stationary phases

Retention parameters of alkaloid standards were determined on different stationary phases, i.e., octadecyl silica, base-deactivated octadecyl silica, cyanopropyl silica, preconditioned cyanopropyl silica, and pentafluorophenyl, using different aqueous eluant systems: acetonitrile-water mixtures; buffered aqueous mobile phases at pH 3 or 7.8; and aqueous eluants containing ion-pairing reagents (octane-1-sulfonic acid sodium salt and pentane-1-sulfonic acid sodium salt) or silanol blockers (tetrabutyl ammonium chloride and diethylamine). Improved peak symmetry and separation selectivity for basic solutes was observed when basic buffer, ion-pairing reagents, and, especially, silanol blockers as mobile phase additives were applied. The best separation selectivity and most symmetric peaks for the investigated alkaloids were obtained in systems containing diethylamine in the mobile phase. The influence of acetonitrile concentration and kind and concentration of ion-pairing reagents or silanol blockers on retention, peak symmetry, and system efficiency was also examined. The most efficient and selective systems were used for separation of the investigated alkaloids and analysis of Fumaria officinalis and Glaucium flavum plant extracts.     

色素的纳米纸色谱分离分析

采用SiO2纳米粒子结合硅烷化处理对滤纸进行改性,以罗丹明B、苏丹红Ⅰ及苏丹红Ⅳ为模型化合物,考察了改性滤纸在分离特性上的差异,对不同粒径纳米粒子、不同硅烷化试剂及不同展开剂的极性进行比较、优化后发现,在同等展开条件下,经改性纳米粒子修饰后的滤纸分离色素的效果得到明显改善,且纳米粒子越小、烷基碳链越长、硅烷化越完全,则...     

Evaluation of silica gel-immobilized phosphorylcholine columns for size exclusion chromatography and their application in the analysis of the subunit structures of fish-egg lectins

Columns of phosphorylcholine (PC) immobilized on silica gel were shown to be useful for size exclusion chromatography (SEC) of proteins. The columns provided good separation of proteins in 50 mM sodium phosphate buffer (pH 6.9) containing 0.25 M NaCl, and there was a linear relationship between the retention times and the logarithmic values of the molecular weights with a correlation coefficient (R²) of 0.978–0.992. The columns were used in analyzing the subunit structures of the rhamnose-binding lectins CSL1, CSL2, and CSL3, isolated from chum salmon (Oncorhynchus keta) eggs. Although the lectins, which are a group of carbohydrate-binding and hydrophobic proteins, behaved anomalously in SEC with conventional matrices, they could be eluted from the immobilized PC columns without non-size-related retention, thereby allowing their molecular weights to be reliably estimated.     

Preparation and evaluation of novel chiral stationary phases based on quinine derivatives comprising crown ether moieties

The C9‐position of quinine was modified by meta‐ or para‐substituted benzo‐18‐crown‐6, and immobilized on 3‐mercaptopropyl‐modified silica gel through the radical thiol‐ene addition reaction. These two chiral stationary phases were evaluated by chiral acids, amino acids, and chiral primary amines. The crown ether moiety on the quinine anion exchanger provided a ligand‐exchange site for primary amino groups, which played an important role in the retention and enantioselectivity for chiral compounds containing primary amine groups. These two stationary phases showed good selectivity for some amino acids. The complex interaction between crown ether and protonated primary amino group was investigated by the addition of inorganic salts such as LiCl, NH₄Cl, NaCl, and KCl to the mobile phase. The resolution results showed that the simultaneous interactions between two function moieties (quinine and crown ether) and amino acids were important for the chiral separation.     

Effect of the residual silanol group protection on the liquid chromatographic resolution of α‐amino acids and proton pump inhibitors on a ligand exchange chiral stationary phase

A new ligand exchange chiral stationary phase (new CSP) containing residual silanol group‐protecting n‐octyl groups on the silica surface was prepared by treating a ligand exchange CSP (original CSP) based on sodium N‐[(R)‐2‐hydroxy‐1‐phenylethyl]‐N‐undecylaminoacetate bonded to silica gel with excess n‐octyltriethoxysilane. The new and original CSPs containing an identical amount of chiral selector were applied to the resolution of α‐amino acids and proton pump inhibitors (PPIs) including omeprazole, pantoprazole, lansoprazole, and rabeprazole. The separation factors (α) and resolutions (R_S) were greater on the new CSP than on the original CSP except for the resolution of asparagine. The trends of the retention factors (k₁) for the resolution of α‐amino acids on the new and original CSPs with the variation of the organic modifier content in aqueous mobile phase were opposite to those for the resolution of PPIs. Removal of the nonenantioselective interactions between the residual silanol groups and the analytes and the improved lipophilicity of the new CSP were proposed to be responsible for the improved chiral recognition ability of the new CSP and the different retention behaviors of the enantiomers between the new and original CSPs.     

Retention modelling of electrostatic and adsorption effects of aliphatic and aromatic carboxylic acids in ion-exclusion chromatography

The retention mechanism of aliphatic and aromatic carboxylic acids in ion-exclusion chromatography has been investigated with consideration of simultaneous electrostatic repulsion effects and hydrophobic adsorption effects. A mathematical relationship between the retention factor of the analyte and the mobile-phase composition (sulfuric acid concentration and percentage of methanol), the type of analyte (pK_a and hydrophobicity) and some physical characteristics of the stationary phase has been derived. Thirteen carboxylic acids (comprising mono- and divalent, aliphatic and aromatic acids) were chosen and used to acquire retention data on three different cation-exchange stationary phases (in which the sulfonate functional groups are bound to polystyrene–divinylbenzene, polymethacrylate or silica) using 14 mobile-phase compositions of varying pH and percent methanol. These retention data were used to derive the parameters necessary to solve the retention model using non-linear regression. In this way, a quantitative measure of the effects of adsorption phenomena on analyte retention were obtained. The model was then used to optimise the separation of nine carboxylic acids.