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A simple and reliable high-performance liquid chromatography method was developed to determine the enantiomeric impurity of tenofovir disoproxil fumarate, an orally bioavailable prodrug of tenofovir, commonly used for the treatment of human immunodeficiency virus and hepatitis B. Tenofovir disoproxil and its enantiomer, were completely separated on a Chiralpak IC column (3 μm, 100 × 4.6 mm, i.d.). The chiral separation was achieved using a mobile phase containing n-hexane, ethanol, methanol, and triethylamine 65/25/10/0.1 (v/v/v/v) at a flow rate of 0.6 mL/min. Ideally, the reversal of enantiomer elution order was achieved on the Chiralpak IC column, to allow the elution of the minor enantiomeric impurity before the major component. Moreover, the proposed method was able to discriminate the active ingredient from the related substances available in the tenofovir disoproxil fumarate raw materials. These compounds were isolated and structurally elucidated by MS and nuclear magnetic resonance. Based on the spectral data, the structures of related substances were confirmed as tenofovir isoproxil monoester and fumaric acid. The high-performance liquid chromatography method was optimized by the design of experiment approach and successfully validated following the International Conference on Harmonization guideline. Proposed method was effectively applied for the quantification of enantiomeric impurity in tenofovir disoproxil fumarate raw materials.

A simple, sensitive, and rapid assay based on hydrophilic interaction liquid chromatography (HILIC) with tandem mass spectrometry was developed and validated for the simultaneous determination of metformin and 13 other oral antihyperglycaemic drugs in human urine using metoprolol as an internal standard. A simple sample clean-up procedure using the "dilute and shoot" approach enabled fast and reliable analysis. Chromatographic separation was performed on a HILIC column using an elution gradient of mobile phase A, composed of 1 mM ammonium formate (pH 5), and mobile phase B, composed of acetonitrile, at a flow rate of 0.35 mL/min. Quantitation was performed on a triple quadrupole mass spectrometer operated in multiple reaction monitoring mode by using electrospray ionization in positive ion mode. The total chromatographic run time was 20 min. Calibration curves for each analyte were linear over concentration ranges of 2-300, 5-400, or 20-500 ng/mL, with a coefficient of determination above 0.99. The method was validated for selectivity, sensitivity, recovery, linearity, accuracy and precision, system suitability, robustness, and stability. Inter-batch and intra-batch coefficients of variation across four validation runs were ≤ 13.62%. The present method was successfully applied for the analysis of metformin and nateglinide in urine samples after their oral administration to healthy human subjects under fasted conditions.

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.

Capillary zone electrophoresis was successfully applied to the enantiomeric purity determination of dexlansoprazole using sulfobutyl ether-β-cyclodextrin and methyl-β-cyclodextrin as chiral selectors. Separations were carried out in a 50 μm, 64/56 cm fused-silica capillary. The optimized conditions included 90 mM phosphate buffer, pH 6.0, containing 30 mM sulfobutyl ether-β-cyclodextrin, 20 mM methyl-β-cyclodextrin as background electrolyte, an applied voltage of 25 kV and a temperature of 16 °C, detection was at 280 nm. The assay was validated for the S-(−)-lansoprazole in the range of 0.2–1.0%. The limit of detection was 0.07%, the limit of quantitation was 0.20%, relative to a total concentration of 4.0 mg mL−1. Intra-day precision varied between 1.72 and 2.07%. Relative standard deviations of inter-day precision ranged between 1.62 and 1.96% for peak area ratio. The assay was applied for the determination of the chiral purity of dexlansoprazole capsules. Recovery in capsules was ranged between 101.7 and 103.1%.