A sensitive HPLC method for the determination of fluoxetine and norfluoxetine in human plasma with fluorescence detection.

A selective, sensitive, and precise HPLC method for the simultaneous determination of fluoxetine (FL) and its N-demethylated metabolite norfluoxetine (NFL) in human plasma has been developed. Following extraction with n-hexane, FL, NFL, and fluvoxamine (internal standard) were derivatized with 7-chloro-4-nitrobenzofurazan (NBD-Cl) under weakly alkaline conditions. NBD derivatives were extracted with chloroform after acidification and chromatographed on a reversed-phase column with gradient elution using acetonitrile and 0.1 mol/L nitric acid (pH 3) solution. Calibration curves were linear over the range of 1.0-100.0 ng/mL and 0.1-50.0 ng/mL for FL and NFL, respectively, with inter- and intraassay precision given by a relative standard deviation (RSD%) of less than 9.2%. The lower limits of quantification were 1.0 ng/mL for FL and 0.1 ng/mL for NFL. Recoveries of FL and NFL from plasma at three different concentrations were assessed. Average recovery was about 100% for both substances. The assay was applied to pharmacokinetic study in 2 healthy volunteers after a single oral administration of 40 mg of FL.

An HPLC method for the determination of lisinopril in human plasma and urine with fluorescence detection.

A selective, sensitive and precise HPLC method with fluorimetric detection has been developed for the assay of lisinopril in human plasma and urine. The clean up of the sample was carried out by solid-phase extraction, firstly with C18-cartridge and secondly with a silica-cartridge. After a pre-column derivatization with fluorescamine, the reaction mixture was chromatographed on C18-column with gradient elution, using methanol and 0.02 M phosphate buffer (pH=3.2). The fluorescamine-lisinopril derivative was detected fluorimetrically by monitoring the emission at 477 nm, with excitation at 383 nm. Linear quantitative response curve was generated over a concentration range of 5-200 ng/ml and 25-1000 ng/ml for plasma and urine samples, respectively. The mean recovery of lisinopril from plasma and urine was 63.41 and 74.08%, respectively. Intra-day and inter-day R.S.D. and R.M.E. values at three different concentrations were assessed. The method was applied for pharmacokinetic study in a healthy volunteer after a single oral dose of 20 mg of the drug.

Halogenated secondary metabolites from Laurencia obtusa.

A new sesquiterpene (1), and a halogenated C15 acetogenin (2), a stereoisomer of neoisoprelaurefucin were isolated from Laurencia obtusa. Four known compounds laurencienyne (3), rogiolenyne B (4), obtusenol (5), and (3E)-dactomelyne (6) were also isolated from this alga. Rogiolenyne B (4) and (3E)-dactomelyne (6) were found for the first from this species. The structures of these compounds were elucidated by spectroscopic methods. The unambiguous assignments of the 1H and 13C NMR spectral data of (5) and 13C NMR data of (6) were also reported for the first time.

An HPLC method for the determination of atorvastatin and its impurities in bulk drug and tablets.

A simple high-performance liquid chromatographic (HPLC) method was developed for the analysis of atorvastatin (AT) and its impurities in bulk drug and tablets. This method has shown good resolution for AT, desfluoro-atorvastatin (DFAT), diastereomer-atorvastatin (DSAT), unknown impurities and formulation excipients of tablets. A gradient reverse-phase HPLC assay was used with UV detection. Some solvent systems prepared using methanol or acetonitrile and water or buffer systems with different pH values were tested. Capacity factors of related substances were calculated at all tested systems. Best resolution has been determined using a Luna C18 column with acetonitrile-ammonium acetate buffer pH 4-tetrahydrofuran (THF) as mobile phase. Samples were eluted gradiently with the mobile phase at flowrate 1.0 ml min(-1) and detected at 248 nm. The proposed method was applied to the determination of impurities and were found to contain 0.057-0.081, 0.072-0.097, 0.608-0.664% of the DFAT, DSAT and total impurity, respectively.

Determination of tyramine in cheese by LC-UV.

An isocratic reversed-phase liquid chromatographic assay for tyramine has been developed. The method is based on the reaction of tyramine with 4-chloro-7-nitrobenzofurazan and measurement of the absorbance at 458 nm after chromatographic separation on a C-18 column. Optimum reaction conditions were investigated. A linear relationship was found between absorbance and concentration over the range 25-300 ng per 10 microl of tyramine. The method was applied to the determination of tyramine in cheese. The cheese sample was homogenized with 5% (w/v) HClO(4) extracted with ethyl acetate-acetone (2:1) and chromatographed on high performance liquid chromatography (HPLC) after derivatization reaction with NBD-Cl. The determination limit was 25 microg/g cheese. The mean recovery of tyramine from cheese was 98.0%.

A new spectrofluorimetric method for the determination of lisinopril in tablets.

An accurate and precise spectrofluorimetric method is presented for the determination of lisinopril based on the formation of a derivative formed with 7-chloro-4-nitrobenzofurazan. The derivatization reaction proceeds quantitatively at pH 8.5-9.0 and 60 degrees C in 70 min when the molar ratio of reagent to the drug is 170. After the extraction with ethyl acetate the fluorescence intensity of the derivative was measured at 528 nm with excitation at 465 nm. Calibration graph is rectilinear over the range of 50-1000 ng/ml with detection and determination limits of 20 and 50 ng/ml, respectively. The regression equation is I(f) = 0.198C-0.299 (r = 0.9999). The method was applied to the commercially available tablets and the results were statistically compared with those obtained by official HPLC method.