Liquid chromatographic separation of the enantiomers of becliconazole and its potential impurities

Sensitivity improvement of circular dichroism detection in HPLC by using a low-pass electronic noise filter: Application to the enantiomeric determination purity of a basic drug

The quality control of chiral drugs requires the determination of their enantiomeric purity. Nowadays, circular dichroism (CD) spectroscopy is gaining increasing importance in pharmaceutical analysis because of the commercially available CD detector in liquid chromatography. The separation of the two enantiomers of a basic drug (efaroxan) was achieved by high performance liquid chromatography using an amylose-derivated column with both UV and CD detections. A baseline-resolved separation (resolution: 5) was obtained after optimization of the mobile phase composition with hexane-ethanol-diethylamine (90:10:0.05; v/v/v). The use of a commercial low-pass electronic noise filter of the CD signal has improved the signal-to-noise ratio by a factor twelve and allowed the quantitation of each enantiomer in the 1.25-300 microg ml(-1) concentration range. The CD linear calibration curve, expressed in terms of stereoisomer height ratio versus concentration ratio, was plotted over the 0.4-6% range. A correlation coefficient greater than 0.999 was obtained by least-squares regression and the limit of detection for the distomer/eutomer ratio was estimated at 0.14%. Although the method validation showed good repeatability on the retention times (RSD < 0.9%), on the peak height ratios (RSD < 8.7%) of each enantiomer only up to 99.2% enantiomeric purity was achieved.

A validated chiral HPLC method for the enantiomeric separation of tolterodine tartarate

An isocratic chiral HPLC method was developed for the separation of tolterodine tartarate enantiomers. The mobile phase consists of n-hexane and isopropyl alcohol in the ratio of 980:20 (v/v) with 1 ml diethylamine and 0.6 ml trifluoroacetic acid. Chiralcel OD-H (250 mm x 4.6mm) column was used at constant room temperature. Flow rate was kept at 0.5 ml/min. This method is capable of detecting the S-isomer up to 0.1 microg/ml. The method was validated in terms of linearity, precision, limit of detection (LOD) and limit of quantification (LOQ).

Enantiomeric resolution of new aromatase inhibitors by liquid chromatography on cellulose chiral stationary phases

Analytical HPLC methods using derivatized cellulose chiral stationary phases were developed for the direct enantioseparation of substituted [1-(imidazo-1-yl)-1-phenylmethyl)]-benzothiazolinone and benzoxazolinone derivatives with one chiral center. Those analogues of fadrozole constitute new potent nonsteroidal inhibitors of aromatase (P450 arom). The separations were made using normal phase methodology with a mobile phase consisting of n-hexane-alcohol (ethanol, 1-propanol, or 2-propanol) in various proportions, and a silica-based cellulose tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H), or tris-methylbenzoate (Chiralcel OJ). The effects of concentration of various aliphatic alcohols in the mobile phase were studied. A better separation was achieved on cellulose carbamate phase compared with the cellulose ester phase. The effects of structural features of the solutes along with the temperature of the column on the discrimination between the enantiomers were examined. Baseline separation (Rs > 1.5) was easily obtained in many cases.

An overview of the recent trends in development of HPLC methods for determination of impurities in drugs

An extensive survey of the literature published in various analytical and pharmaceutical chemistry related journals has been conducted and the high-performance liquid chromatography (HPLC) methods which were developed and used for determination of process-related impurities in drugs have been reviewed. This review covers the time period from 1995 to 2001 during which around 450 analytical methods including all types of chromatographic and hyphenated techniques were reported. HPLC with UV detection was found to be the technique of choice for many workers and more than 200 methods were developed using LC-UV alone. A critical analysis of the reported data has been carried out and the present state-of-art of HPLC for determination of impurities of analgesic, antibiotic, anti-viral, anti-hypertensive, anti-depressant, gastro-intestinal and anti-neoplastic agents has been discussed.

Liquid chromatographic method development for determination of fungicide epoxiconazole enantiomers by achiral and chiral column switching technique in water and soil

High-performance liquid chromatography (HPLC) in both chiral isocratic and achiral-chiral column switching mode was employed for optimization of separation conditions, separation and determination of fungicide epoxiconazole in real samples. Two enantiomers of commercially available triazole fungicide epoxiconazole (BAS 480 F), first registered in 1993, were resolved for the first time on a microcrystalline cellulose triacetate (MCTA). A low-cost home-packed chiral column (150x3 mm, 15-25 microm, MCTA, Merck) enabled baseline enantiomeric resolution of two enantiomers of the fungicide epoxiconazole produced commercially. The effects of concentration of organic modifiers (methanol, ethanol) in mobile phase, flow-rate and temperature were studied. The isocratic chiral HPLC method allows determination of the enantiomers in tap and surface water within the range 1-1000 mg/l by direct injection (20 microl) of the sample. Using the achiral (C18)-chiral (MCTA) column-switching technique and 1-ml sample volume, injection of 0.050 mg/l of epoxiconazole enantiomers can be conveniently determined by UV detection at 230 nm. The same method applied to methanolic soil extracts allows determination of 0.2 mg/kg of epoxiconazole enantiomers in addition to the other 10 commonly used pesticides in fortified soils.

Recent applications of stereoselective chromatography

Some recent applications of stereoselective chromatography in the fields of clinical pharmacy, drug analysis, food, and natural products are reviewed. The review is documented with up-to-date literature, which will assist further expansion of research in these areas.

Chiral discrimination by HPLC and CE and antifungal activity of racemic fenticonazole and its enantiomers

Fenticonazole is a chiral antifungal agent, used in therapy as the racemic mixture. The investigation on the chirality of fenticonazole is reported in this study. rac-Fenticonazole was resolved by HPLC and by capillary electrophoresis (CE). The chiral stationary phase (CSP), used in HPLC, was Daicel OD-H, a commercial phase, which allowed the separate collection of the two enantiomers. The chiral selectors used for CE were some cyclodextrin derivatives. The analysis time required from CE was about the half the HPLC enantioseparation time. The biological activity of the rac-mixture and each individual enantiomer was tested against Cryptococcus neoformans and two Aspergillus nidulans strains. The minimum inhibitory concentration (MIC) evaluation showed that the eutomer was the enantiomer chromatographically more retained and had a longer migration time in the electrophoretic enantioseparation. The CD spectrum of the eutomer showed a positive Cotton effect.

LC separation of ortho and meta isomers of celecoxib in bulk and formulations using a chiral column

A normal phase, isocratic LC method was developed for the separation of positional isomers of celecoxib (I) using a chiral column, Chiralpak-AD. The method is useful for the quantification of ortho (II) and meta (III) forms in bulk drugs and formulation samples of celecoxib. The method has been completely validated and proven to be rugged. The limit of detection (LOD) and limit of quantitation (LOQ) of ortho and meta forms were found to be 38 ng and 116 ng respectively. The active pharmaceutical ingredient was extracted from its finished dosage form (capsule) using ethanol. The percentage recoveries of ortho isomer was found to be 99.8--102.7 and 97.8--103.2 and the percentage recoveries of meta isomer was found to be 99.3--102.6 and 99.7--104 in spiked bulk and formulation samples of celecoxib respectively.