Enantiomeric Resolution of a Chiral Sulfoxide Series by LC on Synthetic Polymeric Columns with Multimodal Elution

Chiral Stationary Phases for Liquid Chromatography: Recent Developments

The planning and development of new chiral stationary phases (CSPs) for liquid chromatography (LC) are considered as continuous and evolutionary issues since the introduction of the first CSP in 1938. The main objectives of the development strategies were to attempt the improvement of the chromatographic enantioresolution performance of the CSPs as well as enlarge their versatility and range of applications. Additionally, the transition to ultra-high-performance LC were underscored. The most recent strategies have comprised the introduction of new chiral selectors, the use of new materials as chromatographic supports or the reduction of its particle size, and the application of different synthetic approaches for preparation of CSPs. This review gathered the most recent developments associated to the different types of CSPs providing an overview of the relevant advances that are arising on LC.

Determination of rabeprazole enantiomers in commercial tablets using immobilized cellulose-based stationary phase

Rabeprazole is one of the latest proton-pump inhibitors used for treatment of several gastrointestinal disorders. For therapeutic applications, rabeprazole has been administered as a mixture of R-(+) and S-(-) enantiomers. Owing to pharmacological and toxicological differences between stereoisomers, chiral recognition has now become an integral part of drug research and development. A simple and rapid liquid chromatographic method for enantioselective separation and determination of R-(+) and S-(-) enantiomers of rabeprazole in bulk drug and pharmaceutical formulations was developed. Chiralpak IC (150 × 4.6 mm, 5 μm) column and μmobile phase containing hexane:ethanol:ethylenediamine (30:70:0.05 v/v) in an isocratic mode yielded baseline separation with resolution greater than 6.0 at 35 °C. Effects of additives and n-hexane were evaluated. Optimized condition was validated as per ICH guidelines. The method has good linearity, high sensitivity with LOD was 0.01 μg/mL and LOQ was 0.03 μg/mL for both enantiomers. Intra-day precision varied between 0.44 and 1.79% for S-(-) enantiomer, 0.65 and 1.97% for R-(+) enantiomer. Relative standard deviations of inter-day precision were less than 1.81% for both enantiomers. The percentage recovery for both enantiomers of rabeprazole ranged between 99.81 and 101.95%, 98.82 and 101.36% in material and tablets, respectively. The method was successfully applied to determine content of each enantiomer in commercial tablets.

New enantioselective LC method development and validation for the assay of modafinil

For the first time, a new, fast and sensitive chromatographic method for the separation and determination of modafinil enantiomers was developed on chiral stationary phase with macrocyclic glycopeptide teicoplanin in the polar organic mode. The effect of the mobile phase composition and column temperature on the retention and enantioseparation were studied. The separation was performed using a Chirobiotic T column (250×4.6mm, 5μm) with methanol and triethylamine (100/0.05, v/v) as the mobile phase at a flow rate of 1.0mL/min, and UV detection at 225nm. The total analysis time is less than 6min, which is faster than the previous chiral HPLC methods (total run time of 12min). Calibration curves were linear (R²>0.999) over a concentration range 5-150μg/mL for each modafinil enantiomer. Limit of detection (LOD) and limit of quantification (LOQ) for (R)-modafinil were 15 and 45ng/mL and for (S)-modafinil were 20 and 60ng/mL, respectively. The recoveries were in the range of 100.5-102.3% with the relative standard deviations ranging from 0.4% to 1.0% for both enantiomers. It was demonstrated that the developed method was selective, precise and robust. The validated method was successfully applied for the separation and determination of modafinil enantiomers in the real samples.

Resolution and determination of enantiomeric purity of new chiral derivatives of xanthones using polysaccharide-based stationary phases

The enantioresolution and determination of the enantiomeric purity of 24 new chiral derivatives of xanthones (CDXs) were investigated on polysaccharide-based chiral stationary phases (CSPs). The tris-3,5-dimethylphenylcarbamates of cellulose and amylose and tris-3,5-dimethoxyphenylcarbamate of amylose were selected as CSPs for this work. The separation of enantiomeric mixtures of CDXs was explored under multimodal elution conditions. All the enantiomeric mixtures of CDXs were enantioseparated with very high enantioselectivity and resolution with α and R(S) ranging from 1.43 to 12.41 and from 1.48 to 10.29, respectively. The best performances were achieved on amylose tris-3,5-dimethylphenylcarbamate stationary phase under polar organic elution conditions. Furthermore the enantiomeric purity for all the CDXs was measured, achieving values higher than 99%. Based on the obtained results, the influence of the mobile phases and structural features of the CSPs and CDXs on chiral discrimination are also discussed.

Recentchiral selectors for separation in HPLC and CE

Enantiomers (stereoisomers) can exhibit substantially different properties if present in chiral environments. Since chirality is a basic property of nature, the different behaviors of the individual enantiomers must be carefully studied and properly treated. Therefore, enantioselective separations are a very important part of separation science. To achieve the separation of enantiomers, an enantioselective environment must be created by the addition of a chiral selector to the separation system. Many chiral selectors have been designed and used in various fields, such as the analyses of drugs, food constituents and agrochemicals. The most popular have become the chiral selectors and/or chiral stationary phases that are of general use, i.e., are applicable in various separation systems and allow for chiral separation of structurally different compounds. This review covers the most important chiral selectors / chiral stationary phases described and applied in high performance liquid chromatography and capillary electrophoresis during the period of the last three years (2008–2011).