Determination of enantiomeric impurity of tenofovir disoproxil fumarate on a cellulose tris(3,5-dichlorophenyl-carbamate) chiral stationary phase and the characterization of its related substances.

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.

Determination of the L-enantiomer of nateglinide in pharmaceutical formulations by micellar electrokinetic chromatography.

An analytical micellar electrokinetic chromatographic method was developed and validated for the determination of the L-enantiomer of nateglinide. Separations were carried out in a 50 µm, 64.5/56 fused-silica capillary. The optimized conditions included 75 mM borate buffer, pH 9.2, containing 50 mM of sodium dodecyl sulfate and 25 mg/mL of methyl-ß-cyclodextrin as background electrolyte, an applied voltage of 20 kV and a temperature of 15, UV detector at 210 nm. The assay was validated for the L-enantiomer of nateglinide. The limit of detection and quantification were 0.07 and 0.2% respectively. Intraday precision was ranged between 0.12 and 1.7%. Interday precision ranged between 0.73 and 1.73%. The assay was applied to the determination of the L-enantiomer of nateglinide in pharmaceutical formulations.