The effect of stationary phase on lipophilicity determination of beta-blockers using reverse-phase chromatographic systems

Evaluation of lipophilicity parameters for basic compounds using different chromatographic stationary phases is presented. An HPLC method for determination of lipophilic molecule-stationary phase interactions was based on gradient analysis. Differences in correlation between the lipophilicity of compounds and experimental chromatographic results obtained in pseudo-membrane systems showed a strong influence of stationary phase structure and physico-chemical properties. beta-Blocker drugs with varying lipophilicity and bio-activity were chosen as test compounds. The stationary phases used for the study were monolithic rod-structure C18 and silica gel octadecyl phase SG-C18 as reference material. The second group was silica gel-based polar-embedded alkylamide and cholesterolic phases. The mobile phase was composed of acetonitrile or methanol with ammonium acetate, and a linear gradient of methanol and acetonitrile in mobile phase was performed. A linear correlation of plots of log k(g) = f(log P) was observed, especially for polar-embedded phases, and this allowed log P(HPLC) to be calculated. The behavior of stationary phases in methanol and acetonitrile buffer showed differences between obtained log P(HPLC) values.     

Chracterization of polyaniline using chromatographic studies

Summary The use of polyaniline as a chromatographic stationary phase has been examined. In the course of this work the column packing material was prepared by coating silica particles with polyaniline chloride. The aniline monomer was polymerised directly on the surface of the silica particles using a chemical method and was characterised using elemental analysis. A series of standard test compounds were employed for chromatographic characterization. The studies revealed information on the practical utility as well as the molecular interactions that took place on the stationary phase.     

新型苯基桥键色谱固定相的热力学性质

将制备的球形苯基桥键型杂化介孔色谱固定相与商品化的C18和苯基键合硅胶固定相对比,研究其热力学性质。以稠环芳烃为例,探讨了溶质在固定相和流动相之间的迁移焓变、迁移熵变等热力学参数的变化。结果表明,与两种商品化的固定相不同,实验制备的苯基桥键固定相不存在明显的焓-熵补偿效应,证实新型桥键固定相分离机理是疏水作用、π-π作用、包结作用等协同作用的结果。     

Ionic liquid-modified silica as a new stationary phase for chromatographic separation

A new stationary phase based on silica modified with 1-methyl-3-propylimidazolium chloride was synthesized and characterized in this paper. A derivative of 1-methyl-3-propylimidazolium chloride was used to chemically modify the surface of silica particles to act as the stationary phase for HPLC. The modified particles were characterized by Fourier Transform Infrared (FT-IR), ¹³C NMR spectroscopy and thermogravimetric analysis (TGA). The surface modification procedure rendered particles with a surface coverage of 0.89 μmol/m² of alkylimidazolium chloride. Columns packed with the modified silica and blank silica particles were tested under HPLC conditions. Preliminary evaluation of the stationary phase for HPLC was performed using aromatic compounds as model compounds. The separation mechanism appears to involve multiple interactions including ion exchange, hydrophobic and electrostatic interactions.     

Validation of the extended Tanaka column characterization protocol by multivariate analysis of chromatographic retention of low‐molecular‐weight analytes on reversed phase columns using methanol and acetonitrile as organic modifiers

The validity of the extended Tanaka column characterization procedure against the retention behavior of 101 analytes of widely differing properties chromatographed on five differing stationary phase chemistries has been established using a chemometric technique called principal component analysis (PCA). It was concluded that the simple and conveniently determined column characterization parameters covered the same space in the PCA loading plot as the retention times for the 101 differing analytes. This confirms that the ten column characterization parameters of the extended Tanaka protocol encode the same information as the retention times of the 101 analytes. Significant selectivity differences were observed between stationary phases and the mobile‐phase modifiers – MeOH and MeCN. PCA contribution plots served as a convenient way to highlight specific selectivity differences between stationary phases. logD values exhibited a poor correlation with retention indicating that retention in RP‐LC is not solely dictated by the analyte's hydrophobicity. The use of MeOH was found to generate greater selectivity differences with the five stationary phases than when MeCN is used.     

Integration of ground aerogel particles as chromatographic stationary phase into microchip

C16 modified and ground monolithic silica aerogel particles in submicrometer size, as a new type of stationary phase was prepared and integrated in polydimethylsiloxane (PDMS) microchip. The aerogel particles were packed into the microfluidic channel using a simple procedure, which does not require any special frit or fabrication step to retain the particles. The subnanoliter volume of samples can be transported through the porous, short length of packing with low pressure (< 3 bar). Food dyes as test components could be separated using low pressure within 6s. A 50-fold preconcentration could be achieved by retaining 100 nL volume of sample on the packing and elution with methanol.     

Preparation and chromatographic properties of a multimodal chiral stationary phase based on phenyl-carbamate-propyl-beta-CD for HPLC

A phenylcarbamate derivative of 2-hydroxypropyl-beta-CD bonded stationary phase was prepared by a previously described method. Its enantiomeric recognition abilities were evaluated as chiral stationary phase (CSP) in normal, polar organic and RP conditions by HPLC. The relevant structural features of the prepared stationary phase which make it an effective chiral selector are discussed. This material seems to have an excellent enantioselectivity for a variety of racemic analytes in the three modes. Hence it can be considered a highly effective multimodal column. Retention factor (k), selectivity (alpha) and resolution (R(s)) were the chosen parameters to describe the column performance. Optimization of these separations was discussed in terms of mobile phase composition, flow rate and structural patterns of the injected analytes.     

Kinetics and equilibria of the chromatographic separation of maltose and trehalose

Trehalose, a nonreducing disaccharide, has been extensively applied to food, cosmetics, and pharmaceutical goods. The resultant solution of trehalose prepared by enzymatic methods includes high amounts of maltose. However, it is quite difficult to separate maltose and trehalose on an industrial scale because of their similar properties. In this paper, a high‐performance resin was selected as a stationary phase to separate trehalose and maltose, and the resolution of these sugars was 0.59. The potential of a cation exchange resin was investigated as the stationary phase in separating trehalose and maltose using deionized water as the mobile phase. Based on the equilibrium dispersive model, the axial dispersion coefficients and overall mass transfer coefficients of maltose and trehalose were determined by moment analysis at two different temperatures, 50 and 70°C. Other parameters, including the column void and the adsorption isotherms, were also determined and applied to simulate the elution curves of trehalose and maltose. The simulated results matched the experimental data, validating the parameters. The optimized parameters are critical to the chromatographic separation of trehalose and maltose on an industrial scale.     

聚合离子液体毛细管气相色谱固定相的性能评价

离子液体作为毛细管气相色谱固定相的选择性和热稳定性是近年人们关注的课题。本文合成了1-烯基-3-苄基咪唑-二(三氟甲基磺酰)亚胺盐(VBIm-NTf2)离子液体并经毛细管柱内聚合制得了聚合离子液体PVBIm-NTf2色谱柱。与VBIm-NTf2色谱柱相比,PVBIm-NTf2色谱柱具有良好的色谱选择性和热稳定性。PVBIm-NTf2色谱柱对Grob试剂、醇混合物、酯混合物和苯系物等都表现了很好的分离能力,并且色谱峰峰形窄且对称。该聚合色谱柱在250 ℃下老化6 h后仍具有良好的分离能力和选择性。本文还测定了PVBIm-NTf2的Abraham溶剂化参数,解析了该固定相与溶质间的相互作用,相关研究国内尚未见报道。研究表明,对常规离子液体进行柱内聚合是改善常规离子液体气相色谱固定相的热稳定性和选择性的有效途径。     

Test to evaluate countercurrent chromatographs. Liquid stationary phase retention and chromatographic resolution

Countercurrent chromatography (CCC) is a liquid chromatography (LC) technique with a special column able to retain a liquid stationary phase while the liquid mobile phase is pumped through. The coil planet centrifuge machines are made of open tube wound on spools. A simple test is proposed. The methanol-water (90:10, v/v)-heptane biphasic system is used with heptane as the mobile phase in the ascending or tail-to-head mode. The methanol-water stationary phase retention volume is measured at different flow-rates and rotor rotation speeds. After every machine equilibration, an alkylbenzene mixture is injected and the retention factors, peak efficiencies and resolution factors are measured or calculated for each solute. The wealth of information contained in the data set obtained is demonstrated. Four coil planet centrifuge machines of very different characteristics and one hydrostatic CCC machine with channels and ducts were submitted to the test. It was shown that the Sf, stationary retention factor, obtained with these machines was linearly dependent on the square root of F, the mobile phase flow-rate [Q. Du, C. Wu, G. Qian, P. Wu, Y. Ito, J. Chromatogr. A 835 (1999) 231-235]. It is shown that the slopes of the Sf versus F(1/2) lines could be related to a minimum rotor rotation, omega(mini), necessary to obtain the hydrodynamic equilibrium. The Sf and F parameters give the mobile phase linear velocity, u. It is shown that u is proportional to the square root of omega, the rotor rotation speed. The slope and intercept of the latter relationship also result in an omega(mini) value coherent with the first one. With the peak efficiencies and chromatographic resolution factors obtained for toluene and hexylbenzene, the parameters: number of plates per tubing turn, machine volume for one plate, and tubing length for one plate, were calculated and compared for the five machines. The internal diameter of the tubing used is shown to be a critical parameter acting on the machine volume and number of tubing turns.     

Reversed-phase liquid chromatographic behavior of the mycotoxins citrinin and ochratoxin A

The reversed-phase (RP) chromatographic behavior of citrinin (CT) and ochratoxin A (OA), the latter introduced as reference substance, were studied as a function of hydrophobicity and silanophilic activities of the stationary phase, pH, type of acid in the eluent, its composition as well as of the column temperature. While OA's affinity to RP materials was not influenced by phase material properties, CT showed a high affinity to hydrophobic phase materials, and its elution order, compared to OA, depended strongly on the phase material chosen. In practice, all octadecyl stationary phases under investigation allowed proper conditions for CT and OA chromatography if judicious selection of influencing parameters, especially a low pH and applying an acid with a pKa<2.3, were chosen.     

High-performance liquid chromatographic stationary phases based on poly(dimethylsiloxane) immobilized on silica

This work describes the preparation and characterization of six stationary phases for high-performance liquid chromatography (HPLC) obtained by deposition of poly(dimethylsiloxane) (PDMS) in HPLC silica particles, followed by immobilization using different processes (thermal treatments, thermal treatment + microwave irradiation, self-immobilization + gamma irradiation and self-immobilization + microwave irradiation). The chromatographic parameters of all the phases were evaluated with a mixture of test compounds having varied natures (acid, basic and neutral). The stability of one of these phases was evaluated in both a neutral mobile phase and a higher pH mobile phase used at an elevated temperature, with promising results.     

咪唑侧基功能化聚离子液体修饰的混合模式色谱固定相的制备及其色谱性能

该文合成了咪唑侧基功能化的离子液体单体1-(4-乙烯基苄基)-3-氰甲基溴化咪唑盐,通过表面引发原子转移自由基聚合将该单体接枝到硅胶表面,制备了一种新型混合模式色谱固定相。采用红外光谱、元素分析及热重分析对其结构进行表征。该色谱固定相具有良好的分离能力。通过研究流动相pH对物质保留的影响,验证了物质在该固定相上存在反相-离子交换保留机理。通过与十八烷基硅烷键合硅胶固定相比较,证实了该聚离子液体固定相对物质保留提供了π-π作用。结果表明,对咪唑侧基功能化是制备新型离子液体固定相的可行方法。     

The gas-liquid chromatographic stationary phase properties of liquid organic salts: Anomalous selectivity variation when employing the Rohrschneider/McReynolds system

The liquid organic salts studied here have wide stable liquid temperature ranges and act as efficient, highly selective gas-liquid chromatographic stationary phases. The effect of carbon number on the gas liquid chromatographic stationary phase properties of this series of tetra-n-butylammonium n-alkylsulfonate salts was evaluated by the well-known Rohrschneider/McReynolds system. Several problems arose when attempting to characterize these polar liquid organic salts employing this system. The specific retention volumes for the polar selectivity probes were generally not affected by an increase in the carbon number for the series studied here. However, the specific retention volumes for the n-alkane retention index markers increased dramatically as the anion carbon number was increased. The overall effect was a net decrease in the calculated McReynolds constants with increasing carbon number, although the true selectivity of the different stationary phases remained constant. Additionally, the specific retention volumes of the basic test probe, pyridine, showed large erratic variations and, in some cases, was not recovered from the columns. The results suggest the possibility of on-column chemical reactions occurring with some of these salts, and an alternative test probe, 2,6-dimethylpyridine (lutidine) is proposed to eliminate this problem. As McReynolds constants are presently the most commonly used parameters for predicting retention and gas chromatographic stationary phase selection, it is important that workers are aware of the inherent limitations of this scheme.     

Mobile phase effects on retention on a new butylimidazolium-based high-performance liquid chromatographic stationary phase

A new HPLC stationary phase based on n-butylimidazolium bromide has been characterized by a linear solvation energy relationship (LSER) approach in the binary acetonitrile/water mobile phases. The retention properties of the stationary phase were systematically evaluated in terms of intermolecular interactions between 28 test solutes and the stationary phase. The results and further comparisons with conventional reversed phase system confirm that retention properties are similar to phenyl phases in acetonitrile/water mixtures. The results obtained with acetonitrile/water mixtures are also compared with results obtained using methanol/water mixtures.     

Gas chromatographic behaviour and pharmacological activity of neuroleptica

Biological activity in vitro, quantified as equilibrium inhibition constants to the dopamine receptor, of a series of neuroleptica are correlated with parameters describing polar and apolar interactions of these molecules with the receptor. Gas-chromatographic retention indices on stationary phases of different polarity are compared with parameters that are classically used in such quantitative structure/activity studies. To describe a polar interactions, a series of classical parameters such as several valence molecular indices and log k′ in a reversed-phase h.p.l.c. system are included; retention indices on the apolar stationary phase, OV101, are used as the gas-chromatographic (g.c.) parameter. To take the more specific polar interactions into account, quantum-chemical charge parameters such as the dipole moment and the charge on atoms directly involved in the interaction were calculated. Retention indices on the more polar phase OV17 are taken as the g.c. parameter for polar interactions. It is shown that the retention indices on OV101 can replace classical parameters describing aspecific or apolar interactions. The retention indices of OV17 do not correlate with biological activity and are worse than the charge parameters.