Development and validation of a capillary electrophoresis method for the determination of escitalopram and sensitive quantification of its enantiomeric impurity in formulations.

A rapid capillary zone electrophoresis method has been developed capable of quantifying 0.05% of R-enantiomer and assaying the main component in escitalopram formulations. Many parameters influencing enantioseparation were investigated, which include chiral selectors, buffer composition and pH, applied voltage, capillary length, temperature, and rinsing procedure. Optimal separation conditions were obtained by using a 25 mM phosphate buffer at pH 7.0, containing 1.6% (w/v) sulfated-ß-cyclodextrin with short-end injection at 0.5 psi for 5 s. Online UV detection was performed at 205 nm. A voltage of -20 kV was applied and the capillary temperature was kept at 25°C. Separation was achieved in less than 2 min. The method was further validated, including robustness, stability of the solution, selectivity, linearity (escitalopram from 0.25 µg/mL to 600 µg/mL, y = 1528.3 × +1812.9; R² = 0.9999), LOD and LOQ (0.08 and 0.25 µg/mL, respectively), precision and accuracy. The proposed method was then applied to the quality control of the bulk sample and tablets of escitalopram (10 mg).

Development of a validated capillary electrophoresis method for enantiomeric purity control and quality control of levocetirizine in a pharmaceutical formulation.

A chiral capillary electrophoresis method has been developed for the quantification of 0.1% of the enantiomeric impurity (dextrocetirizine) in levocetirizine and determination of both in pharmaceuticals using sulfated-ß-cyclodextrins (CDs) as chiral selector. Several parameters affecting the separation were studied such as the type and concentration of chiral selectors, buffer composition and pH, organic modifier, mixtures of two CDs in a dual system, voltage, and temperature. The optimal separation conditions were obtained using a 50 mM tetraborate buffer (pH 8.2) containing 1% (w/v) sulfated-ß-CDs on a fused-silica capillary. Under these conditions, the resolution of two enantiomers was higher than 3. To validate the method, the stability of the solutions, robustness (two level half fraction factorial design for 5 factors using 19 experiments [2(n-1)+3]), precision, linearity (dextrocetirizine 0.25-2.5 µg/ml, R(2) = 0.9994, y = 0.0375x + 0.0008; levocetirizine 15-100 µg/ml, R(2) = 0.9996, y = 0.0213x + 0.0339), limit of detection (0.075 µg/ml, 0.03% m/m), limit of quantification (0.25 µg/ml, 0.1% m/m), accuracy (dextrocetirizine 84-109%, levocetirizine 97.3-103.1%), filter effect, and different CD batches were examined. The validated method was further applied to bulk drug and tablets of levocetirizine.

Development and validation of a chiral capillary electrophoresis method for assay and enantiomeric purity control of pramipexole.

A rapid method for the enantioseparation of pramipexole and its R-enantiomer has been developed by capillary electrophoresis. The influence of chemical and instrumental parameters was investigated including the type and concentration of chiral selectors, buffer composition and pH, co-ions, applied voltage, capillary length and temperature. Optimal separation conditions were obtained using a 50 mM phosphate buffer (pH 2.8) containing 25 mM carboxymethyl-ß-cyclodextrin on a fused-silica capillary. Online UV detection was performed at 262 nm. A voltage of 25 kV was applied, and the capillary temperature was kept at 25°C. Hydrodynamic injection was performed at 3.45 kPa for 5.0 s. The separation of enantiomers was achieved in <6.5 min. The method was further validated in terms of stability of solutions, selectivity, linearity (both pramipexole and R-enantiomer, R(2) >0.995), LOD and LOQ (0.91 and 2.94 µg/mL, respectively), repeatability (RSD<1.5%) and accuracy (pramipexole, 100.4%; R-enantiomer, 100.5%). The proposed method was then applied to two kinds of pramipexole dihydrochloride monohydrate commercially available tablets, immediate release tablets (1.50 and 0.125 mg) and sustained release tablets (0.52 mg), to quantify the main component in the tablets. The amount of distomer could be quantified in bulk sample materials.

Enantiomeric N-methyl-4-piperidyl benzilates as muscarinic receptor ligands: Radioligand binding studies and docking studies to models of the three muscarinic receptors M1, M2 and M3.

Benzilic ester derivatives with a basic moiety like N-methyl-4-piperidyl benzilates are potential drugs for the treatment of urinary incontinence, duodenal and gastric ulcers and Parkinson's disease. The effect of structural variations of chiral N-methyl-4-piperidyl benzilates was investigated using radioligand binding studies on muscarinic receptors (M1-M3). The results of the binding studies demonstrate that the absolute configuration and the aromatic substituent of benzilates have an influence on muscarinic affinity and selectivity. In this regard, (S)-configuration of benzilates and hydrophilic aromatic substituents seems to enhance muscarinic affinity. A model of the receptor ligand complex for N-methyl-4-piperidyl benzilates was obtained by molecular modelling. Both the affinity of enantiomeric benzilic esters and the subtype selectivity for muscarinic receptors are comprehensively explained by this model.