A rapid HPLC method for determination of zolpidem and its degradation product in tablets using a monolithic column.
A simple, accurate reverse phase high-performance liquid chromatographic method, utilizing a monolithic silica column, for determination of zolpidem hemitartrate and its degradation product in tablet dosage form was developed. Analysis was achieved on the monolithic, C18 (100 mm, 3.9 mm) column, in isocratic mode with acetonitrile-NaH2PO4 (pH 7.0; 0.01 M; 35:65, v/v) as mobile phase and a flow rate of 2.5 mL/min at room temperature with UV detection at 245 nm. Diazepam was applied as an internal standard. The retention time of zolpidem and its degradation product was 2.14 and 1.89, respectively. Calibration curve was linear in the range of 0.12-5 µg/mL and the recovery values were found to be 97-101%. The limit of quantitation was determined 0.12 μg/mL. The relative standard deviation values of intraday and interday studies were calculated as 0.13-1.1% and 0.54-1.3%, respectively.
Rapid Determination of Sildenafil Citrate in Pharmaceutical Preparations Using Monolithic Silica HPLC Column
Abstract A simple, rapid, and sensitive high performance liquid chromatography (HPLC) method has been developed and validated for the determination of sildenafil citrate in pharmaceutical preparations. The method was developed utilizing a 100 × 4.6 mm I.D. monolithic silica column and an isocratic elution of 60:40, v/v acetonitrile/water. The elution of the analyte was monitored at 292 nm with a flow rate of 2.0 mL/min. All analyses were conducted at ambient temperature. Linearity was observed in the concentration range from 50–3000 ng/mL, with a correlation coefficient (R 2) greater than 0.999. The limit of detection was 25 ng/mL. Parameters of validation prove the precision of the method and its applicability for the determination of sildenafil citrate in pharmaceutical tablet formulations. The method is fast (less than 1 min) and is suitable for high throughput analysis of the drug.
Development of a stereospecific radioimmunoassay for the analysis of zopiclone and metabolites in urine.
A sensitive and specific radioimmunoassay has been developed, allowing the stereospecific detection of nanogram amounts of (+)- and (-)-enantiomers of zopiclone and its major metabolites in urine, without prior extraction or purification. Antisera were obtained from two series of four rabbits, immunized with optically pure (+)- and (-)-N-hemisuc-cinyldesmethylzopiclone, conjugated to bovine serum albumin according to the active ester method. The assay was stereospecific, allowing discrimination between the two enantiomers of N-desmethylzopiclone with mutual cross-reactivities below 2%. Substantial cross-reaction was observed with the parent compound, although lower than expected, and to a lesser extent with the N-oxide metabolite. A selection of hypnotics, anxiolytics, antidepressants and some other widely used drugs did not interfere with the assay (< 0.1%), when tested at a concentration level of 10 micrograms/ml. The sensitivity of the assay was 50 pg/ml and 10 pg/ml for the (+)- and (-)-enantiomers, respectively. The binding assay described here was used to evaluate the stereoselective excretion pattern of zopiclone. Analysis of cumulative excretion samples from a volunteer revealed a mean metabolic excretion ratio (+)/(-) of 2.2, ranging from 1.7 (7 h) to 4.4 (36 h) A mean excretion ratio (+)/(-) of 2.5 +/- 1 was calculated after analysis of urine samples from 20 patients receiving zopiclone as a hypnotic daily.