Evaluating “Fast” Micellar Monolithic Liquid Chromatography for High-Throughput Quantitative Structure−Retention Relationship Screening

Evaluating micellar liquid chromatographic methods on octadecyl particle-based and monolithic columns to predict the skin permeation of drug and cosmetic molecules

A micellar liquid chromatographic method was developed to assist in the modeling of the skin permeability of pharmaceutical and cosmetic compounds. The composition of the mobile phase was determined by means of a two-factor central composite design, after which it was tested on both a particle-based and monolithic column. The latter provided the opportunity to increase the flow rate from 1 to 8 mL/min without reaching too high backpressures. The micellar conditions allowed analyzing a large test set of compounds with diverse characteristics with just one mobile-phase composition. The obtained experimental chromatographic descriptors besides two sets of theoretical molecular descriptors were used to model the skin permeability coefficient log K_p, applying multiple linear regression and partial least squares regression approaches. The micellar method on the monolithic column provided useful models with similar or even slightly better performance parameters than the method on the particle-based column. Furthermore, a much faster analysis can be achieved when applying a flow rate of 8 mL/min, making the micellar monolithic method ideal to estimate skin permeability.

Established HPLC fraction analysis to predict furanocoumarin-based herb-drug metabolic interactions

An attempt was made in this study to predict the potential for metabolic interactions of herbal extracts of drugs from their chromatographic profiles in reverse-phase high-performance liquid chromatography (RP-HPLC). Twenty-nine structurally related furanocoumarin compounds with known inhibitory interactions with cytochrome P450 3A (CYP3A), which is important for phase-I drug metabolism, were selected as a model system. A sigmoidal relationship was established between the CYP3A inhibitory potency (y) and the RP-HPLC total peak response unit (R(u), x) as y = 85.36 x (14.86 + x)⁻¹ with a correlation coefficient of 0.63. The sigmoidal curve could be divided into three ranges designated low, medium and high risk that were used to indicate the relative inhibitory potency of the metabolic interactions of herbs or traditional Chinese herb medicines with CYP3A. These predictive classifications provide information or might be useful for 'risk category' decisions concerning herb-drug interactions.

Surfactant-bound monolithic columns for CEC

A novel anionic surfactant bound monolithic stationary phase based on 11-acrylaminoundecanoic acid is designed for CEC. The monolith possessing bonded undecanoyl groups (hydrophobic sites) and carboxyl groups (weak cationic ion-exchange sites) were evaluated as a mixed-mode stationary phase in CEC for the separation of neutral and polar solutes. Using a multivariate D-optimal design the composition of the polymerization mixture was modeled and optimized with five alkylbenzenes and seven alkyl phenyl ketones as test solutes. The D-optimal design indicates a strong dependence of electrochromatographic parameters on the concentration of 11-acrylaminoundecanoic acid monomer and porogen (water) in the polymerization mixture. A difference of 6, 8 and 13% RSD between the predicted and the experimental values in terms of efficiency, resolution and retention time, respectively, indeed confirmed that the proposed approach is practical. The physical (i.e. morphology, porosity and permeability) and chromatographic properties of the monolithic columns were thoroughly investigated. With the optimized monolithic column, high efficiency separation of N-methylcarbamates pesticides and positional isomers was successfully achieved. It appears that this type of mixed-mode monolith (containing both chargeable and hydrophobic sites) may have a great potential as a new generation of CEC stationary phase.

Surfactant-bound monolithic columns for separation of proteins in capillary high performance liquid chromatography

A surfactant-bound monolithic stationary phase based on the co-polymerization of 11-acrylamino-undecanoic acid (AAUA) is designed for capillary high performance liquid chromatography (HPLC). Using D-optimal design, the effect of the polymerization mixture (concentrations of monomer, crosslinker and porogens) on the chromatographic performance (resolution and analysis time) of the AAUA-EDMA monolithic column was evaluated. The polymerization mixture was optimized using three proteins as model test solutes. The D-optimal design indicates a strong dependence of chromatographic parameters on the concentration of porogens (1,4-butanediol and water) in the polymerization mixture. Optimized solutions for fast separation and high resolution separation, respectively, were obtained using the proposed multivariate optimization. Differences less than 6.8% between the predicted and the experimental values in terms of resolution and retention time indeed confirmed that the proposed approach is practical. Using the optimized column, fast separation of proteins could be obtained in 2.5 min, and a tryptic digest of myoglobin was successfully separated on the high resolution column. The physical properties (i.e., morphology, porosity and permeability) of the optimized monolithic column were thoroughly investigated. It appears that this surfactant-bound monolith may have a great potential as a new generation of capillary HPLC stationary phase.

Quantitative structure-(chromatographic) retention relationships

Since the pioneering works of Kaliszan (R. Kaliszan, Quantitative Structure-Chromatographic Retention Relationships, Wiley, New York, 1987; and R. Kaliszan, Structure and Retention in Chromatography. A Chemometric Approach, Harwood Academic, Amsterdam, 1997) no comprehensive summary is available in the field. Present review covers the period of 1996-August 2006. The sources are grouped according to the special properties of kinds of chromatography: Quantitative structure-retention relationship in gas chromatography, in planar chromatography, in column liquid chromatography, in micellar liquid chromatography, affinity chromatography and quantitative structure enantioselective retention relationships. General tendencies, misleading practice and conclusions, validation of the models, suggestions for future works are summarized for each sub-field. Some straightforward applications are emphasized but standard ones. The sources and the model compounds, descriptors, predicted retention data, modeling methods and indicators of their performance, validation of models, and stationary phases are collected in the tables. Some important conclusions are: Not all physicochemical descriptors correlate with the retention data strongly; the heat of formation is not related to the chromatographic retention. It is not appropriate to give the errors of Kovats indices in percentages. The apparently low values (1-3%) can disorient the reviewers and readers. Contemporary mean interlaboratory reproducibility of Kovats indices are about 5-10 i.u. for standard non polar phases and 10-25 i.u. for standard polar phases. The predictive performance of QSRR models deteriorates as the polarity of GC stationary phase increases. The correlation coefficient alone is not a particularly good indicator for the model performance. Residuals are more useful than plots of measured and calculated values. There is no need to give the retention data in a form of an equation if the numbers of compounds are small. The domain of model applicability of models should be given in all cases.