Selectivity In High-performance Liquid Chromatography Research Articles

Recent developments of monolithic and open-tubular capillary electrochromatography (2017-2019).

Capillary electrochromatography, which combined the high selectivity of high-performance liquid chromatography and the high separation efficiency of capillary electrophoresis, is an attractive separation tool. In this review, the developments on monolithic and open tubular capillary electrochromatography during 2017 to August 2019 are summarized. Considering the development of novel stationary phases is the most active research field in capillary electrochromatography, monolithic capillary electrochromatography is classified according to the polymer-based and hybrid monolithic columns, while open-tubular capillary electrochromatography is categorized by cyclodextrin, silica, polymer, nanomaterials, microporous materials, and biomaterials-based open tubular columns.

Improvement of sensitivity and selectivity of high-performance liquid chromatography for anti-retroviral drugs (non-reverse transcriptase inhibitors) by diamond-electrode electrochemical and fluorescence detection

The new non-reversed transcriptase inhibitor (NRTI) drugs for treatment of acquired immunodeficiency syndrome (AIDS) are reported. An improvement in the sensitivity and selectivity of high-performance liquid chromatography was obtained by diamond electrode–electrochemical detector and fluorescence detector owing to different structural information. The four anti-retroviral NRTI drugs (abacavir, didanosine, lamivudine and zidovudine) were separated on a CapcellPak C18 UG120 column (250 mm × 4.6 mm I.D., 5 μm) with an acetonitrile–25 mM potassium dihydrogenphosphate buffer (pH 8.0; 1:9, v/v) as the mobile phase. We applied dual detection (electrochemical detection and florescence detection) for improving the peak identification and also for improved selectivity, which assisted monitoring by trace-volume samples (e.g., plasma). The electrochemical detector, equipped with a diamond electrode, was set at 2000 mV (applied voltage) and the fluorescence detector was set at excitation wavelength 275 nm and emission wavelength 315 nm. The detection limits of the four NRTIs in spiked plasma were 1–100 ng/ml by electrochemical detection and 5–10 pg/ml by fluorescence detection. The calibration graphs were linear up to 20 μg/ml by electrochemical detection and 10 μg/ml by fluorescence detection. This is the first report of LC analysis of NRTIs by electrochemical detection, also combined with fluorescence detection. The detection limits of didanosine, lamivudine and zidovudine were improved 20-fold by electrochemical detection and 500-fold by fluorescence detection compared to previous reports on UV detection. The selectivity was also improved by dual detection. The proposed method was applied to the preliminary monitoring of NRTIs in plasma.

Enhancement of molecular-shape selectivity in high-performance liquid chromatography through multi-anchoring of comb-shaped polymer on silica

Poly(octadecylacrylate) having plural trimethoxysilyl groups in the side chain (co-ODA n ) was newly synthesized and immobilized onto silica through these groups. The liquid chromatographic behavior of silica-supported co-ODA n (Sil-co-ODA n ) was investigated and compared with that of Sil-ODA n , in which poly(octadecylacrylate) was immobilized through a terminal trimethoxy group at one side of the polymer main chain. Sil-co-ODA n showed higher selectivity for molecular shape, especially molecular planarity of PAHs than Sil-ODA n .

Analysis of active ingredients and preservatives in creams by capillary electrochromatography (CEC)

Capillary electrochromatography (CEC) is an analytical method of growing interest to the pharmaceutical industry. Because CEC is a combination of high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) it has the advantages of the high selectivity of HPLC and the high efficiency of CE. The capillaries can be packed with different packing materials. The mixed-mode phase consisting of a strong cation exchanger and alkyl chains on the silica surface has some advantages over conventional reversed-phase (RP) packing materials. In this article the authors describe the use of CEC to separate the active ingredients and preservatives in creams from different manufactures. On the basis of the high efficiency of CEC it was possible to develop one isocratic method for all the compounds in the different samples. The method was validated with regard to identification, reproducibility, linearity, limit of detection, and quantitation.

Optimization of selectivity in high-performance liquid chromatography using desirability functions and mixture designs according to prisma

A computer program for the mobile phase optimization of high-performance liquid chromatography (HPLC) is described. The desirability function technique combined to the prisma mixture design was employed to enhance the quality of HPLC separations. The use of statistical models to predict the behaviour of retention times ( t R) and band broadening at the different eluent compositions obtained by prisma was examined for dansyl amides and coumarins. The study showed that the dependence between the eluent composition and t R values of dansyl amides and coumarins can be expressed using quadratic regression models with a high degree of accuracy. Band broadening given by means of the band width at half-height ( w h) was described by a linear regression model. Both models were used in calculating and predicting the resolution ( R s) in various solvent combinations. The desirability function converted the calculated ( R s) value into the desirability value ( D), and the overall optimum was then defined by means of the overall desirability. The optimal eluent mixtures for the separation of compounds were easily read from the contour plot inside the horizontal plane of the prisma model. A good separation was achieved using the optimized solvent combination. Depending on the aims of the optimal separation, the program allows either optimization of critical pairs or achieving the overall optimum giving a reasonable separation for as many compounds as possible.

Optimization of Selectivity in High-Performance Liquid Chromatography Using Mixture-Design Statistical Techniques: Overview and Software for Data Analysis

Abstract Optimization of separations in high-performance liquid chromatography (HPLC) is dependent on several factors: the proper choice of variables; a definition of criteria for a suitable separation; a rational strategy for examining the effects of these variables; and an efficient analysis of the data using manual methods or computer software. The selection of variables and, strategy for optimization is discussed in this paper, and a detailed description of a versatile software package for data analysis is presented along with provisions for obtaining the actual FORTRAN source code. The original mixture-design statistical software has been expanded and enhanced to accomodate data from both isocratic and gradient elution separations, single or multiple stationary phases, and other variables, such as temperature or pH. The software can be used to predict a single optimum set of conditions for a particular separation, and also to calculate the actual separation quality under any set of conditions bounded...

Column selectivity in high-performance liquid chromatography of substituted gem-dimethylcyclopropanes

High-performance liquid chromatographic (HPLC) separation of a series of gem-dimethylcyclopropanes was carried out in a variety of mobile phase and stationary phase systems. Comprehensive evaluation of column selectivity was made to identify chromatographic conditions under which various isomers could be resolved. In normal-phase HPLC on silica, retention data appeared to serve as good indicators for predicting relative polarity of the compounds in the solvent systems studied. For most cases, excellent baseline resolution of cis-trans mixtures was attained. The cis and trans components of chrysanthemol (CS) and ethyl chrysanthemate, however, were separated only with mobile phases of hexane and hexane-isopropanol (98:2), respectively. In reversed-phase HPLC, geometrical isomers of all but chrysanthemol were well resolved on octadecylsilica despite the poor selectivity of a propylphenylsilica column for these isomers under conditions used. The latter reversed-phase separation on propylphenylsilica succeeded only in two cases (RU-11679 and permethrin). Elution of cis and trans isomers in reversed-phase HPLC followed the same order as in normal-phase HPLC, except for the halogenated compounds where a reversal in elution order was observed. Among chiral stationary phases studied, the chiral polymeric packings, (+)-poly(triphenylmethylmethacrylate) exhibited the highest selectivity for compounds containing aromatic groups on ester moieties. The halogen substituents in permethrin and baythroid seemed to have adverse effects on the chiral recognition process. In HPLC on β-cyclodextrin-bonded silica, separations of diastereomeric (+)- cis- and (+)- trans-allethrin, and cis- and trans-chrysanthemol demonstrated unique examples of unusual selectivity of β-cyclodextrin-bonded silica for isomers that virtually remained indiscernible by all other HPLC methods investigated. The percentage of β-cyclodextrin in the bonded phase had dramatic influence on the α values of certain isomeric pairs. Increasing the percentage β-cyclodextrin in the bonded phase somewhat favored the separation of some optical antipodes.