title: Low level determination of dorzolamide and its de-ethylated metabolite in human plasma by liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry.
abstract: A sensitive and specific method for the determination of dorzolamide (I) and its de-ethylated metabolite (II) in human plasma has been developed utilizing high pressure liquid chromatography (HPLC) with tandem mass spectrometric (MS/MS) detection. The analytes and internal standard (III) were isolated from the deproteinized pH 8.0 buffered plasma, using a liquid-liquid extraction with a mixture of ethyl acetate, toluene, and isopropanol. The analytes were then back extracted into 0.085% phosphoric acid (200 microliters) and after washing the acidic extract with hexane, the organic layer was discarded and a fraction (50 microliters) of the acid extract was injected into the LC/MS/MS system. The MS/MS detection was performed on a PE Sciex API III tandem mass spectrometer using a heated nebulizer interface. Multiple reaction monitoring of the parent-->product ion combinations of m/z 325-->199, 297-->199, and 397-->306 were used to quantify I, II, and III, respectively. The assay was validated in the concentration ranges of 0.5-100 and 2.5-100 ng ml-1 of plasma for I and II, respectively. The precision of the assays, expressed as coefficients of variation (C.V.%), were less than 10% over the entire concentration range, with adequate assay specificity and accuracy. The LC/MS/MS method provided a 10-fold increase in the sensitivity of I over the previously reported HPLC/UV method [1].
authors.affiliation: Merck Research Laboratories, West Point, PA 19486, USA.
authors.forename: M L
authors.initials: ML
authors.lastname: Constanzer
authors.forename: C M
authors.initials: CM
authors.lastname: Chavez
authors.forename: B K
authors.initials: BK
authors.lastname: Matuszewski
mesh_terms: D000959:Antihypertensive Agents / Q000097:blood* / Q000378:metabolism; D002257:Carbonic Anhydrase Inhibitors / Q000097:blood* / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002853:Chromatography, Liquid; D006801:Humans; D013058:Mass Spectrometry; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013056:Spectrophotometry, Ultraviolet; D013449:Sulfonamides / Q000097:blood* / Q000378:metabolism; D013876:Thiophenes / Q000097:blood* / Q000378:metabolism
chemical_list: D000959:Antihypertensive Agents; D002257:Carbonic Anhydrase Inhibitors; D013449:Sulfonamides; D013876:Thiophenes; C062765:dorzolamide