Experimental Capacity Factors Research Articles

Discrimination between enantioselective and non-selective binding sites on cellobiohydrolase-based stationary phases by site specific competing ligands

A systematic study was performed to investigate the influence of cellobiose or lactose on the enantioselective retention behaviour of some β-blockers in liquid chromatography using Cellobiohydrolase (CHB) I from Trichoderma reesei or Cellobiohydrolase 58 from Phanerochaete chrysosporium immobilized on silica as stationary phases. The results revealed that the retention could be described by the function k′ x=k′ ns,x + k′ es,x 1+ [ competitor] K d where the observed capacity factor corresponds to the sum of an enantioselective mode being influenced by a site specific competing ligand (competitor) and a non-selective mode unaffected by the competitor. A non-constrained non-linear least-square regression gave in all cases virtually identical nondisplacable capacity factors ( k′ ns) for both enantiomers of the same drug. The experimental capacity factors ( k′ x,C ) of the enantiomers all show a close fit to the adapted function. The K d values calculated for the competitor were also virtually identical for each pair of enantiomers and were in accordance with K i data determined for the competitors in classical enzyme kinetics experiments, demonstrating that one unique site; namely, the catalytic site, was responsible for the enantioselective binding. Similar results were obtained with the resolution of rac-alprenolol and rac-metoprolol on CBH I phase.

Application of an artificial neural network in chromatography—retention behavior prediction and pattern recognition

Layered feed-forward neural networks are powerful tools particularly suitable for the analysis of nonlinear multivariate data. In this paper, an artificial neural network using improved error back-propagation algorithm has been applied to solve problems in the field of chromatography. In this paper, an artificial neural network has been used in the following two applications: (1) To model retention behavior of 32 solutes in a methanol–tetrahydrofuran–water system and 49 solutes in methanol–acetonitrile–water system as a function of mobile phase compositions in high performance liquid chromatography. The correlation coefficients between the calculated and the experimental capacity factors were all larger than 0.98 for each solute in both the training set and the predicting set. The average deviation for all data points was 8.74% for the tetrahydrofuran-containing system and 7.33% for the acetonitrile-containing system. 2). To classify and predict two groups of different liver and bile diseases using bile acid data analyzed by reversed-phase high performance liquid chromatography (RP-HPLC). The first group includes three classes: healthy persons, choledocholithiasis patients and cholecystolithiasis patients; the total consistent rate of classification was 87%. The second group includes six classes: healthy persons, pancreas cancer patients, hepatoportal high pressure patients, cholelithiasis patients, cholangietic jaundice patients and hepatonecrosis patients; the total consistent rate of classification was 83%. It was shown that artificial neural network possesses considerable potential for retention prediction and pattern recognition based on chromatographic data.

Description and prediction of retention in normal-phase high-performance liquid chromatography with binary and ternary mobile phases

The suitabilities of several earlier reported models for description and prediction of retention in normal-phase systems with mobile phases comprised of two organic solvents — a polar and a non-polar one — were tested on the chromatographic behaviour of phenylurea herbicides and alkyl-, aryl- and nitrophenols as sample solutes with a silica-gel column and 2-propanol, n-heptane and dioxane as mobile phase components. With few exceptions, the data obtained from the best-fit three-parameter retention equation differe from the experimental capacity factors at less than 0.1, or 2%, and for most compounds the fit is better than 1%. Of the two two-parameter equations derived from theoretical models, one failed to describe the retention behaviour. The fit of the other two-parameter equation to the retention data of phenols is slightly inferior than with the three-parameter equation. The differences between the fitted data and the experimental capacity factors of substituted phenylureas were ⩽ 0.2, or 5%. Three-parameter equations were suggested to describe the retention behaviour in three-component mobile phases either at a constants sum or at a consant ratio of the two stronger solvents in ternary mobile phases. To fit the three-component data at any combination of concentrations of the three solvents with the error comparable to that in binary mobile phases, a nine-parameter equation is necessary. Suitability of these equations to describe the experimental behaviour of substituted phenylureas and phenols was verified in ternary mobile phases with various concentrations of 2-propanol, dioxane and n-heptane. Finally, a method was suggested for the prediction of retention in ternary mobile phases with varying concentration ratios of the two polar solvents from the parameters of best-fit equations in binary mobile phases and a single experimental capacity factor in a ternary mobile phase. For most capacity factors, the error of prediction was lower than 0.2 or 5%. Dried solvents were used to improve the reproducibility of the results and the temperature was controlled to ±0.1°C in all experiments. With these precautions, differences between the original retention volumes and the data from repeated experiments measured after ten months of use of the column in the system tested were less than 0.2 ml for 85% of the values compared.

Retention models of capacity factor with different compositions of organic modifier in RP-HPLC

A Chromatographic retention behavior of five deoxyribonucleosides (dCyd, dUrd, dGuo, dThd, and dAdo) with respect to the mobile phase composition was studied under isocratic conditions of reversed phase High Performance Liquid Chromatography (RP-HPLC). The volume fraction (F) of organic modifier was changed from 0.05 to 0.30, and to 0.12 for methanol and acetonitrile, respectively. The experimental data of nitro and steroid compound were also considered for comparison of five retention models with various class of samples. The Langmuir-type retention model (k′= A+B/F) with two parameters shows excellect agreements between the experimental capacity factors and calculated values although the values by the log-scale quadratic model with three parameters (log k′= LF2+MF+N) are closer. Unlike the other four retention models, the slope B of the Langmuir-type retention model can characterize the properties of solute and organic modifier simultaneously. For each solute, the intercepts A calculated for acetonitrile and methanol as organic modifiers are coincident closely.

Influence of Alcohol Organic Modifiers Upon the Association Constants and Retention Mechanism for Aromatic Compounds in Micellar Liquid Chromatography

Abstract Solute-micelle association constants and partition coefficients between stationary, aqueous, and micellar phases have been determined for a group of benzene derivatives and polycyclic aromatic hydrocarbons with sodium dodecyl sulphate and hexadecyltrimethylammcnium bromide by Micellar Liquid Chromatography (MLC) with an octylsilica column using micellar mobile phases in absence and in the presence of organic modifiers (methanol, n-propanol, and n-butanol). The retention mechanism of these compounds in the chromatographic system has been studied by comparing experimental capacity factors and selectivity coefficients with those theoretically calculated assuming a direct transfer mechanism. When the surfactant concentration in the mobile phase is increased, a tendency to a change from a three-partition equilibrium mechanism to a direct transfer of solutes from micellar to stationary phase is observed for both surfactants. This change was favored when: (1) the hydrophobic character of the solute incr...

A model describing the effect on retention of the addition of alcohols to the mobile phase in micellar liquid chromatography

A physico-chemical model relating the capacity factor of a solute to micellized surfactant and organic modifier concentrations in micellar liquid chromatography with hybrid eluents is proposed. The equation derived from this model and some simplified equations were tested by using retention data in micellar mobile phases containing hexadecyltrimethylammonium bromide and sodium dodecyl sulphate as surfactants and n-propanol and n-butanol as organic modifiers. Good agreement between calculated and experimental capacity factors was found and the use of this model to predict the retention behaviour of solutes in micellar liquid chromatography is proposed.

Phase Equilibria of Alkanes in Natural Gas Systems. 3. Alkanes in Carbon Dioxide

A chromatographic technique was used to measure experimental capacity factors for the n-alkanes from C9H20 to C36H74 in CO2 from 308.2 to 348.2 K and from 100 to 240 bar. Infinite dilution activity coefficients, γi∞, were calculated for the solid n-alkanes (C24H50 to C36H74) utilizing regular solution theory to characterize the stationary phase. This allowed the estimation of solubilities from capacity factors for the solid n-alkanes in CO2.

7-azetidinylquinolones as antibacterial agents. 2. Synthesis and biological activity of 7-(2,3-disubstituted-1-azetidinyl)-4-oxoquinoline- and -1,8-naphthyridine-3-carboxylic acids. Properties and structure-activity relationships of quinolones with an azetidine moiety.

A series of 7-(2,3-disubstituted-1-azetidinyl)-1,4-dihydro-6-fluoro-4- oxoquinoline- and -1,8-naphthyridine-3-carboxylic acids, with varied substituents at the 1-, 5-, and 8-positions, was prepared to study the effects on potency and physicochemical properties of the substituent at position 2 of the azetidine moiety. The activity of the title compounds was determined in vitro against Gram-positive and Gram-negative bacteria, and the in vivo efficacy of selected derivatives was determined using a mouse infection model. The X-ray crystal structures of 6b, 6c, and 6d were found to be in reasonable agreement with the corresponding AM1 calculated geometries. Correlations between antibacterial potency of all the synthesized 7-azetidinylquinolones and naphthyridines and their calculated electronic properties and experimental capacity factors were established. Antibacterial efficacy and pharmacokinetic and physicochemical properties of selected derivatives were compared to the relevant 7-(3-amino-1-azetidinyl) and 7-(3-amino-3-methyl-1-azetidinyl) analogues (for Part 1, see: J. Med. Chem. 1993, 36, 801-810). A combination of a cyclopropyl or a substituted phenyl group at N-1 and a trans-3-amino-2-methyl-1-azetidinyl group at C-7 conferred the best overall antibacterial, pharmacokinetic, and physicochemical properties to the azetidinylquinolones studied.

Possibilities of determination and prediction of solute capacity factors in reversed-phase systems with pure water as the mobile phase

A sorption and an elution experimental method were developed and tested for the determination of solute capacity factors in pure water as the mobile phase in reversed-phase systems. The experimental values determined by the sorption method are generally higher than those determined by the elution method, but the two types of values are strongly correlated. These correlations may be used for corrections of the experimental capacity factors to suit either chromatographic or sorption conditions. The log k′ dependencies on methanol concentration are adequately described by quadratic equations for various pesticides tested over a range of mobile phase compositions from 2 to 90% methanol in water, but the extrapolation to zero methanol concentration yields systematically lower extrapolated capacity factors, k′ H 2O . The extrapolated values depend strongly on the range of the experimental k′ and on the range of methanol concentrations used for the determination of the experimental data points, and neither linear nor quadratic extrapolation yield correct k′ H 2O values. The accuracy of predicted extrapolated k′ H 2O improves as the concentration range of methanol approaches zero, but the time of determination and experimental difficulties increase simultaneously. The accuracy of the predicted k' H 2O values from the low methanol concentration range can be improved using correlations with the k′ H 2O values determined experimentally. The correlation equations are determined for a set of (at least three) standard compounds and apply only for a given sorbent. Correlations of log k′ H 2O with solute lipophilic indices, n ce, yield better predictions than similar correlations with logarithms of solute solubilities, with comparable errors in the predicted k′ H 2O values as for the values extrapolated from the data measured in the range of medium methanol concentrations.

Ion-exchange-desolvation mechanism on octadecyl silica using anionic hydrophobic pairing ions

The adsorption isotherms for several anionic hydrophobic pairing ions in water on ODS Hypersil are reported. The previously proposed retention model involving ion exchange and desolvation is assessed for various ionised basic solutes by comparing experimental capacity factors with those calculated on the basis of the proposed model as a function of pairing-ion concentration. Relative ion-exchange constants are calculated and shown to be constant for all pairing ions and solutes. Addition of acetonitrile as organic modifier in aqueous solution is shown to alter both the loading and isotherm shape for both sodium laurylsulphate and cetrimide. Using appropriate solutes, it is shown that the ion-exchange-desolvation model applies quantitatively to the mixed solvents studied.