Molecular Shape Selectivity for Polycyclic Aromatic Compounds on a Core–Shell Octadecylsilica Stationary Phase at Subambient Column Temperatures

Molecular shape selectivity for polycyclic aromatic compounds on a core–shell-type octadecylsilica (ODS) phase at subambient column temperatures was studied in reversed-phase liquid chromatography. The plate height on the core–shell ODS column was relatively stable at subambient column temperatures when compared with that of a conventional ODS column. In order to compare the sample diffusivities in the conventional and core–shell ODS columns, van Deemter plots were prepared. The plate height of the core–shell column was significantly lower than that of conventional column, suggesting an advantageous feature of the core–shell-type stationary phase especially at a high flowrate of the mobile phase. An enhanced molecular shape recognition capability of the core–shell ODS phase was also confirmed at subambient column temperature. The result could be consistent with an improved shape selectivity as normally observed on conventional ODS phases at low temperatures, however, the enhanced molecular shape recognition capability of the core–shell phase enables a good separation between benz[a]anthracene and chrysene at subambient column temperatures. Similar improved shape selectivities for terphenyl isomers were also confirmed on the core–shell phase.

     

Electrochemically Controlled Liquid Chromatography on Conducting Polymer Stationary Phases

Abstract

Electrochemically controlled high performance liquid chromatography (EC/HPLC) using a conducting polymer stationary phase, has been investigated in the present paper. Polypyrrole coated reticulated vitreous carbon (RVC) particles have been employed as the stationary phase. Chromatographic characterization has been carried out using various molecular probes. The results indicate that chromatographic retention can be altered by the imposition of small electrical potentials on the stationary phase and that such effects can be used to improve the separation of certain compounds.     

Cyanobiphenyl-Mesogened Liquid Crystalline Polymer Bonded on Silica as the Stationary Phase with Shape and Polarity Recognition for LC

Cyanobiphenyl-mesogened liquid crystalline polymer is bonded on silica by surface-initiated atom transfer radical polymerization and is used as the stationary phase for liquid chromatography. Various instrumental analyses such as elemental analysis, X-ray photoelectron spectroscopy and differential scanning calorimetry were used for its characterization. The stationary phase exhibits multiple characteristics of low hydrophobicity, low hydrophobic selectivity, polarity recognition and shape selectivity in the separation of polyaromatic hydrocarbons and polar neural aromatic compounds. Temperature and mobile phase composition were confirmed to have effects on the chromatographic behavior. Isomers of polyaromatic hydrocarbons and carotenes are well separated on the stationary phase.     

Ionisation Effects in the Reversed Phase Liquid Chromatographic Separation of Thyromimetic Iodoamino Acids

Abstract

The influence of ionisation equilibria on the retention behaviour of iodoamino acids and related compounds on micro-particulate octadecylsilica supports has been examined. The chromatographic data for these ionogenic solutes have been discussed in terms of current concepts for reversible solvophobic interactions with the hydrocarbonaceous stationary phase. This treatment permits the conditional effects of the mobile phase composition and pH on solute retention to be assessed and the relationship between the molecular surface area of a solute and its retention to a non polar stationary phase evaluated.     

Valuation of environmental influence of recently invented high-performance liquid chromatographic method for hypoglycemic mixtures of gliflozins and metformin in the presence of melamine impurities: Application of molecular modeling simulation approach

Molecular modeling is the science of representing molecular structures numerically and simulating their behavior with the equations of quantum and classical physics. Coupling molecular modeling and simulation with chromatographic resolution for pharmaceutical products constitutes a new technique in pharmaceutical analysis. An innovative high-performance liquid chromatographic (HPLC) methodology was developed for the quantification of metformin hydrochloride (MET), empagliflozin (EMP), and canagliflozin (CAN) in bulk, laboratory-developed combinations, pharmaceutical tablets, and in the presence of melamine. Chromatographic separation was accomplished using a Symmetry column with 0.03 M potassium dihydrogen phosphate buffer and 0.02 M heptane sulphonic acid: acetonitrile as the mobile phase. Molecular modeling using molecular operating environment software was applied to properly select the stationary phase suitable for the developed HPLC method. Additionally, molecular modeling estimates and validates binding between the studied analytes and the stationary phase to clarify and explain the chromatographic separation and elution order. In accordance with the International Conference of Harmonization recommendations, the method was validated in terms of linearity, accuracy, precision, and selectivity. The linearity ranges (μg/ml) were 200–1500 (MET), 2–15 (EMP), and 20–150 (CAN) and the limit of detection values were in the ranges of 0.17–54.58 μg/ml. Analysis of pharmaceutical tablets using the suggested approach yielded satisfactory outcomes. As a result, it might be used in quality control laboratories to analyze the aforementioned medications.     

Preparation and chromatographic evaluation of new branch-type diamide-embedded octadecyl stationary phase with enhanced shape selectivity

A novel branch-type diamide-embedded octadecyl stationary phase was prepared by facile amidation. The preparation of this new phase involves the synthesis of new bifunctional silane ligand and surface modification of spherical silica via anchoring of silane coupling agent. The obtained diamide-embedded octadecyl stationary phase demonstrated excellent hydrophobic selectivity, as well as enhanced shape and planarity selectivity in comparison to commercial polymeric and monomeric C₁₈ phases, respectively, as revealed by the systematic investigation into its liquid chromatographic retention of isomeric polycyclic aromatic hydrocarbons. The applicability of this new stationary phase was further testified by the effective separation of isomeric compounds belong to different chemical classes, including chain isomers of alkylbenzenes, and positional isomers of substituted aromatics. An in-depth analysis of the separation mechanisms other than molecular shape recognition involved in the new stationary phase was performed using a linear solvation energy relationships model and compared with its monoamide and pure C₁₈ counterparts correspondingly. The performance of the new stationary phase in quantitative analysis of phenols from real-world samples was also evaluated.     

Chitin as Stationary Phase in Thin-Layer Chromatography–Application of Chromatographic Process Optimization Theory for Chitin Layers

Abstract

This paper describes initial of two basic theories of adsorption thin-layer chromatography potimization namely thermodynamic adsorption theory and theory based on mass action law, so called Snyder s theory in chromatographic systems containing chitin as stationary phase on wchich various amino acids were chromatographed. The results obtained were comparable to those obtained for analogous chromatographic systems containing silica gel as stationary phase. Comparison of applicability of these theories for well investigated silica gel and for not enough investigate chitin will permit to draw introductory conclusions about the processes carrying in the chromatographic systems containing chitin as stationary phase.     

High-Performance Liquid Chromatography of some Bases and Nucleosides on Alkylphosphonate-Modified Magnesia-Zirconia Column

ABSTRACT

The high-performance liquid chromatographic behavior of some bases and nucleosides was studied on a new reversed-phase stationary phase, alkylphosphonate-modified magnesia-zirconia. The effect of mobile phase variable such as methanol content, ionic strength and pH on their behavior was investigated. It was found that the retention behavior of the bases and nucleosides on the new stationary phase is similar to that on ODS stationary phase. The retention mechanism on the new stationary phase was also discussed. The separation of some bases and nucleosides was accomplished on the new stationary phase.     

Role of the Dissolution Mechanism in Determining Chromatographic Separation of Biogenic Amines from Their Precursors and Metabolites by HPLC-EC

Abstract

The current study was designed to elucidate the theoretical basis for chromatographic separation of biogenic amines on an octadecyl-silica (C-18) reverse phase column by determining the intermolecular forces between the solute and the stationary phase. The solutes mass transfer diffusion and the heat effect between solutes and stationary phase were assessed by a convenient method. This study demonstrates that the dissolution mechanism plays a major role in the process of chromatographic resolution of biogenic amines and their precursors and metabolites by HPLC-EC.     

Reversed-Phase Ion-Pair Chromatography Of Antihistamine Drugs

Abstract

A reversed-phase ion-pair chromatographic separation of some antihistamine drugs is presented. The stationary phase consists of 1-pentanol or methylene-chloride adsorbed on a CH-10 column and the mobile phase of a phosphate buffer containing cyclohexylsulphamate and dimethyl-octylamine. It is concluded that this method is a valuable complement to a partition chromatographic method reported in an earlier publication.     

Evaluation of deuterium isotope effects in normal-phase LC-MS-MS separations using a molecular modeling approach

Molecular modeling of stationary phases presents a unique challenge because there is little available experimentally derived structural information. Verified interaction mechanisms at a molecular level with analytes are also rare. Molecular mechanics calculations using the Tripos force field were carried out to qualitatively and quantitatively assess stationary phase interactions. Binding energy values of -15.40, 15.28, -12.53, and -12.34 kcal/mol, respectively, are obtained for olanzapine (OLZ), OLZ-D3, des-methyl olanzapine (DES), and DES-D8 that corresponded to the retention behavior of the four compounds observed using liquid chromatography-mass spectrometry (MS)-MS. The model explains, semiquantitatively, the deuterium isotope effect in the normal-phase chromatographic separation of these compounds.     

A Hydrochlorothiazide-Imprinted Polymer

ABSTRACT

Hydrochlorothiazide (HCT) is a medicine commonly used as a diuretic. A series of HCT-imprinted polymers were prepared using 4-vinylpyridine or methacrylic acid or none as a functional monomer. Liquid chromatographic analysis using the polymers as a stationary phase showed that 4-vinylpyridine was suitable for synthesizing HCT-selective polymers. It appeared that the sulfonamide groups on HCT molecule could interact with 4-vinylpyridine through ionic interaction, and thus could be used as a functional group for molecular imprinting. The prepared HCT-specific polymers should have applications for clinical analysis of HCT.     

Synthesis and Chromatographic Evaluation of Perfluorooctyl Stationary Phase for Separation of Basic Compounds

Fluorinated stationary phases provide unique separation effect on basic compounds, due to the fluorine atoms, and pentafluorophenyl stationary phases (PFPs) are the most widely used. Considering that some fluoroalkyls have higher fluorine contents than PFPs do, it is speculated that fluoroalkyl stationary phases should have potential new applications. Herein, we synthesized a silica-based stationary phase bonding perfluoroctyl (FC8) proved by characterization through elemental analysis and solid-state ¹³C cross-polarization/magic-anglespinning nuclear magnetic resonance. The chromatographic behavior of the stationary phase was evaluated with test compounds. In addition, to further study the applicability of FC8 materials, Corydalis decumbens (Thunb.) Pers. fraction, considered as a challenging medicine on reversed-phase chromatography columns, was chosen as a test sample. Results demonstrated that the FC8 stationary phase had better and more satisfactory separation performance than the PFP stationary phase on basic compounds.

     

Characterization of a Cellulose Trisphenylcarbamate/1-Octyl-3-methylimidazolium Tetrafluoroborate Mixture as GC Stationary Phase: Thermodynamic Parameters and LSER Methodology

A novel cellulose trisphenylcarbamate/1-octyl-3-methylimidazolium tetrafluoroborate [CTPC/[OcMIM]BF₄] gas chromatographic stationary phase was prepared and characterized utilizing thermodynamic parameters and LSER methodology. The results revealed that the interaction model of each probe molecule on the CTPC/[OcMIM]BF₄ stationary phase was invariable within the temperature range studied because of an excellent linear relationship between lnk and 1/T for each probe molecule. The chromatographic retentions of all probe molecules on the CTPC/[OcMIM]BF₄ stationary phase were enthalpy-driven processes. The main interaction forces of the stationary phase with probe molecules are hydrogen bonding interactions, dispersive interactions and dipole–dipole interactions. Moreover, the contribution of each interaction is in the order of hydrogen bonding interaction > dispersive interaction > dipole–dipole interaction. The mixture of CTPC and [OcMIM]BF₄ used as capillary gas chromatography stationary phase had high column efficiency and good film-forming ability, which was suitable for the separation of both nonpolar and polar compounds. Particularly the separation efficiencies of aromatic amines on CTPC/[OcMIM]BF₄ are superior to those on the commercial SE-54 column.

     

Molecular Shape Selectivity for Polycyclic Aromatic Compounds on a Core–Shell Octadecylsilica Stationary Phase at Subambient Column Temperatures

Molecular shape selectivity for polycyclic aromatic compounds on a core–shell-type octadecylsilica (ODS) phase at subambient column temperatures was studied in reversed-phase liquid chromatography. The plate height on the core–shell ODS column was relatively stable at subambient column temperatures when compared with that of a conventional ODS column. In order to compare the sample diffusivities in the conventional and core–shell ODS columns, van Deemter plots were prepared. The plate height of the core–shell column was significantly lower than that of conventional column, suggesting an advantageous feature of the core–shell-type stationary phase especially at a high flowrate of the mobile phase. An enhanced molecular shape recognition capability of the core–shell ODS phase was also confirmed at subambient column temperature. The result could be consistent with an improved shape selectivity as normally observed on conventional ODS phases at low temperatures, however, the enhanced molecular shape recognition capability of the core–shell phase enables a good separation between benz[a]anthracene and chrysene at subambient column temperatures. Similar improved shape selectivities for terphenyl isomers were also confirmed on the core–shell phase.     

Phase-distribution chromatography (PDC) of polystyrene

A chromatographic technique is described where the stationary phase is a layer of a very high molecular polystyrene fraction (M = 10⁷) on glass beads (ballotines). The mobile phase is cyclohexane passing the column at a constant temperature below the theta-temperature. A polystyrene sample of sufficiently low molecular weight (M ≤ 10⁶) injected as a small plug at the top of the column is fractionated because the distribution between the mobile and the stationary phase depends on the molecular weight. Since the large molecules preferentially remain in the stationary phase, the smaller molecules leave the column first. The fractionation effect is inverse to that found in GPC experiments. The separation efficiency is rather good and can be described by a simple thermodynamic theory.     

The Use of an α-Cyclodextrin Mobile Phase in the Thin-Layer Chromatographic Separation of Ortho,Meta, and Para Substituted Phenols

Abstract

An aqueous solution of α-cyclodextrin (cyclohexaamylose) is demonstrated to be a very effective mobile phase in thin-layer chromatographic separations. The chromatographic behaviors of twenty-six substituted phenolic and naphtholic compounds using polyamide thin-layer stationary sheets are described. The R_f values were found to be dependent upon both the structural features of the phenolic compounds and the concentration of α-cyclodextrin in the mobile phase. A possible mechanism that accounts for the observed chromatographic behavior is presented. The advantages and disadvantages of the aqueous α-cyclodextrin mobile phase over the traditional pure or mixed organic solvent systems typically employed are discussed.     

Chromatographic behavior of new deazapurine ribonucleosides in hydrophilic interaction liquid chromatography

The chromatographic behavior of new biogenic purine nucleosides in hydrophilic interaction liquid chromatography was examined on three different stationary phases, namely bare silica, and amide‐ and cyclofructan‐based stationary phases. The effects of buffer concentration, pH and acetonitrile‐to‐aqueous‐part ratio in the mobile phase on retention and peak shape were assessed. The retention coefficients and peak symmetry values substantially differed with respect to analytes´ structures, stationary phase properties and mobile phase composition. The bare silica column was unsuitable for these compounds under the chromatographic conditions tested due to very broad and asymmetrical peaks. Furthermore, the cyclofructan‐based stationary phase provided almost Gaussian peak shapes of all deazapurine nucleosides under most conditions tested. Therefore, the cyclofructan‐based stationary phase is the most suitable choice for the chromatographic analysis of nucleosides.     

Stationary phases

Summary A simple method for the preparation of a silica immobilized pentafluorophenyldimethylsilyl ligand (PFPS phase) is described. The chromatographic properties of this material have been compared with those of a phenyldimethylsilyl stationary phase (PDMS phase). Differentation of the results shows that the PFPS has the character of a reversed and a normal phase, whereas the PDMS phase may be only used in reversed-phase liquid chromatography.

---

Stationäre Phasen3. Darstellung und Charakterisierung einer Pentafluorphenyldimethylsilyl-Phase

---

Part 2; see [1]     

Evaluation of Alkyl Bonded Silica and Solvent Phase Modifiers for the Efficient Elution of Basic Drugs on HPLC

Abstract

Nine representative drugs were used to evaluate the effects of alkyl bonded stationary phases containing type A and type B silica and the effects of an amine modifier on the efficiency of high performance liquid chromatographic elution of basic and acidic drugs. The theoretical plate count and asymmetry factor of the eluted peaks were compared to that of acetophenone as a reference to the maximal efficiency of each system evaluated. Zorbax^R C₈ was used as the stationary phase prepared from type A silica and Zorbax RX^R was used as the stationary phase prepared from the type B silica. The theoretical plate count and asymmetry factor of acetophenone was observed to be the same on both columns when analyzed in an acidic aqueous/acetonitrile mobile phase. An improvement in the efficiency and peak shape of the amine containing compounds was observed using the Zorbax RX^R stationary phase as compared to the efficiency and peak shape of these compounds on the Zorbax^R C₈ stationary phase. Interestingly, the acidic compounds salicylic acid and mefenamic acid showed better peak shapes on the Zorbax RX^R column than on the Zorbax C₈. For all drugs studied the theoretical plate count and asymmetry factor was better on both the Zorbax^R C₈ and the Zorbax RX^R stationary phases when the amine modifier triethylamine was used in the mobile phase. Except for salicylic acid, the theoretical plate count and asymmetry factor for each drug was similar on the Zorbax^R C₈ and the Zorbax RX^R columns when the amine modifier