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A sensitive, selective, simple and fast HPLC method based on the formation of derivative with fluorescamine was developed for the determination of memantine (ME) in human plasma. Separation was achieved on a CN column (200 mm×4.6 mm) using acetonitrile-10 mM orthophosphoric acid containing 1 mL/L triethylamine (45:55, v/v) at a flow rate of 1 mL/min. Emission and excitation wavelengths were 480 and 380 nm, respectively. Amantadine was used as an internal standard. Calibration graphs were rectilinear over the range of 1.0-100.0 ng/mL. Limit of detection and limit of quantification were found to be 0.3 and 1.0 ng/mL, respectively. Intra-day and inter-day relative standard deviation values were found to be <2.03%. Average recovery was also found to be around 94%. Proposed method was applied for the pharmacokinetic study in a healthy volunteer after a single oral administration of 20 mg of ME.

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For the first time, a carboxyl group derivatization assay has been developed and validated for the determination of the cholesterol-lowering drug rosuvastatin in human serum at picogram level by high-performance liquid chromatography with fluorescence detection. The assay procedure involved a simple one-step liquid-liquid extraction of rosuvastatin with lovastatin as internal standard from serum with an ethyl acetate-methyl tertiary buthyl ether (1:1) mixture. After pre-column derivatization with 9-anthryldiazomethane at room temperature for one hour, the reaction mixture was injected onto a Phenomenex, Synergi C18 column (250 × 4.6 mm, 4 µ i.d.). The analytes were separated with a mobile phase composed of acetonitrile-water in gradient elution mode and detected at λ(em) = 410 nm, exciting at 366 nm. Calibration curves were constructed in concentration range of 0.01-20.0 ng/mL and limit of detection and limit of quantification values were found to be 0.68 and 2.30 pg/mL, respectively. To test suitability of the developed methods for clinic use, the pharmacokinetics of rosuvastatin were investigated after oral administration of a 20 mg rosuvastatin film tablet to a healthy volunteer and maximum plasma concentration, time to reach that concentration and elimination half life were found to be 17.5 ng/mL, 3.5 h and 18.09 h, respectively.

A new, sensitive and selective spectrofluorimetric method has been developed for the determination of duloxetine (DLX) in capsule and spiked human plasma. DLX, as a secondary amine compound, reacts with 7-chloro-4-nitrobenzofurazon (NBD-Cl), a highly sensitive fluorogenic and chromogenic reagent used in many investigations. The method is based on the reaction between the drug and NBD-Cl in borate buffer at pH 8.5 to yield a highly fluorescent derivative that is measured at 523 nm after excitation at 478 nm. The fluorescence intensity was directly proportional to the concentration over the range 50-250 ng/mL. The reaction product was also measured spectrophotometrically. The relation between the absorbance at 478 nm and the concentration is rectilinear over the range 1.0-12.0 µg/mL. The methods were successfully applied for the determination of this drug in pharmaceutical dosage form. The spectrofluorimetric method was also successfully applied to the determination of duloxetine in spiked human plasma. The suggested procedures could be used for the determination of DLX in pure form, capsules and human plasma being sensitive, simple and selective.