Correlation between hydrophobicity and retention data of several antihistamines in reversed-phase liquid chromatography with aqueous-organic and micellar-organic mobile phases

The Quantitative Characterization of Chemical Modification of Sodium Dodecyl Sulphate Micellar Solutions and Retention Model in Micellar Liquid Chromatography

The micelle solutions of sodium dodecyl sulphate (NaDS) modified by simultaneously presence of different aliphatic alcohols and an inorganic salt have been quantitatively characterized by the values of critical micelle concentrations, the degrees of counter-ion binding and electrostatic potentials of surface. The obtained characteristics of hybrid micelles and the coefficients of modifier distribution between aqueous solution and micellar pseudophase were used to develop a conceptual retention model in micellar liquid chromatography (MLC). The new retention model takes into account the microenvironment changes of an analyte when it goes from the hybrid micellar eluent to a modified surface of alkyl-bounded sorbent.

Solute–solvent interactions in micellar liquid chromatography

The solvation parameter model has been applied to the characterization of hybrid micellar chromatographic systems with mixtures of sodium dodecyl sulfate (SDS) and pentanol as mobile phases. Retention factors for 22 compounds in two groups, phenethylamines and antihistamines, were used for the characterization of the systems after the calculation of their Abraham descriptors. Three equations were developed as multiple linear regressions using Abraham descriptors and properties, such as log Poct and polar surface area to correlate the retention factors. A group of 30 data points was used as an independent test set to assess the predictive capability of the equations. Micellar chromatographic systems were compared against other separation systems using principal components analysis. Conventional RPLC chromatography using mobile phases with high amounts of organic solvents are close to the micellar mobile phases that only use small amounts of alcohol.

Optimization by factorial design of a capillary zone electrophoresis method for the simultaneous separation of antihistamines

A 3(2) full factorial design was used to optimize the experimental conditions of a capillary zone electrophoresis method aimed at achieving simultaneous separation and quantification of the antihistamines brompheniramine, chlorpheniramine, cyproheptadine, diphenhydramine, doxylamine, hydroxyzine, and loratadine according to their therapeutic group. A statistical program, SPSS, was used to calculate the mathematical model with which to obtain the response surface. Critical parameters such as pH and applied voltage were studied to evaluate their effect on resolution and on efficiency. Optimum separation conditions were phosphate buffer pH 2.0, 5kV, and 2psis(-1) at 214nm. The analysis time was below 9min and the theoretical plates were between 6000 and 63,000N. Calibration curves were prepared for the antihistamines. The limits of detection were 4-14ngmL(-1), which allow their quantification in pharmaceuticals. The RSD% of each antihistamine was fairly good. Up to seven antihistamines belonging to the antihistaminic H(1)-receptor group were separated in the same electropherogram. The proposed method was then applied to the determination of antihistamines in pharmaceutical, urine, and serum samples with recoveries in agreement with the stated contents.

Simultaneous optimization of the resolution and analysis time in micellar liquid chromatography of phenyl thiohydantoin amino acids using Derringer's desirability function

The chemometrics approach was applied for simultaneous optimization of resolution and analysis time of nine phenyl thiohydantoin amino acids in micellar liquid chromatography. Derringer's desirability function, a multi-criteria decision making method, was tested for the evaluation of the two different chromatographic performance goals. The effect of five experimental parameters on a chromatographic response function formed using two sigmoidal desirability functions was investigated. The sigmoidal functions were used to transform the optimization criteria, resolution and analysis time, into the desirability values. The factors studied were the concentration of sodium dodecyl sulfate, alkyl chain length of the alcohol used as the organic modifier, organic modifier content, mobile phase pH and temperature. The experiments were performed according to a face-centred cube response surface experimental design to map the chromatographic response surface. Then, calculated chromatographic response functions were fitted to a polynomial model. The obtained regression model was characterized by both descriptive and predictive ability (R2 = 0.988 and R(2)cv = 0.973). The model was verified, as good agreement was observed between the predicted and experimental values of the chromatographic response function in the optimal condition. Based on the results of the study, combination of response surface mapping with Derringer's desirability function allows to predict the best operating condition in micellar liquid chromatography of phenyl thiohydantoin amino acids with respect to resolution and analysis time.

Multi-criteria decision making in micellar liquid chromatographic separation of chlorophenols

Simultaneous optimization of separation quality and analysis time of the micellar liquid chromatography of nine chlorophenol isomers was investigated. The effect on retention of three experimental parameters was studied using multivariate analysis. The factors studied were the concentration of sodium dodecyl sulfate, propanol content, and pH of the mobile phase. The experiments were performed according to the face-centered cube central composite design and the inverse form of the experimental retention times of analytes was fitted to polynomial models. The results of the analysis of variance showed that the models obtained explain over 99% of the variance observed in the chromatograms. The good predictive ability of the models was verified by high correlation coefficient (R2 > 0.99) and F ratio values for the plots of predicted cross-validated versus experimental retention times. The study showed that the use of the Pareto-Optimality method, an approach from multi-criteria decision making, allows selection of the best possible combinations of separation quality and analysis time in micellar liquid chromatography of chlorophenols.

Micellar versus hydro-organic mobile phases for retention-hydrophobicity relationship studies with ionizable diuretics and an anionic surfactant

Logarithm of retention factors (log k) of a group of 14 ionizable diuretics were correlated with the molecular (log P o/w) and apparent (log P(app)) octanol-water partition coefficients. The compounds were chromatographed using aqueous-organic (reversed-phase liquid chromatography, RPLC) and micellar-organic mobile phases (micellar liquid chromatography, MLC) with the anionic surfactant sodium dodecyl sulfate (SDS), in the pH range 3-7, and a conventional octadecylsilane column. Acetonitrile was used as the organic modifier in both modes. The quality of the correlations obtained for log P(app) at varying ionization degree confirms that this correction is required in the aqueous-organic mixtures. The correlation is less improved with SDS micellar media because the acid-base equilibriums are shifted towards higher pH values for acidic compounds. In micellar chromatography, an electrostatic interaction with charged solutes is added to hydrophobic forces; consequently, different correlations should be established for neutral and acidic compounds, and for basic compounds. Correlations between log k and the isocratic descriptors log k(w), log k(wm) (extrapolated retention to pure water in the aqueous-organic and micellar-organic systems, respectively), and psi0 (extrapolated mobile phase composition giving a k = 1 retention factor or twice the dead time), and between these descriptors and log P(app) were also satisfactory, although poorer than those between log k and log P(app) due to the extrapolation. The study shows that, in the particular case of the ionizable diuretics studied, classical RPLC gives better results than MLC with SDS in the retention hydrophobicity correlations.

Potential of immobilized artificial membrane chromatography for lipophilicity determination of arylpropionic acid non-steroidal anti-inflammatory drugs

Molecular lipophilicity can be expressed by logP or more conveniently by logk, i.e. determined by the traditional shake-flask technique or by liquid chromatography. The logk of 11 arylpropionic non-steroidal anti-inflammatory drugs (NSAIDs) was determined at pH 7.4 of the eluent using two stationary phases i.e. octadecylsilane phase and an immobilized artificial membrane (IAM.PC.MG) packing. The chromatographic retention factors extrapolated to 100% aqueous phase (logk(wODS) and logk(wIAM)) were correlated with n-octanol/water lipophilicity parameters (logP) and with n-octanol/water partition coefficients corrected for ionization at pH 7.4 (logD7.4). In this series of compounds, significant linear correlations (r>0.94) between the chromatographic parameters (logk(wIAM)) and the reference lipophilicity data (logP and logD7.4) were described. Moreover, regression analysis between the lipophilicity parameters and some pharmacokinetic data for the drugs under study were performed. The logk(wIAM) parameter over n-octanol/water partition data seems to provide a good model to obtain lipophilicity parameters of arylpropionic acid NSAIDs for quantitative structure-activity relationships studies.