A sensitive LC–MS/MS method for the quantitative analysis of the Echinacea purpurea constituent undeca-2-ene-8,10-diynoic acid isobutylamide in human plasma
2011
Goey, Andrew K.L. | Sparidans, Rolf W. | Meijerman, Irma | Rosing, Hilde | Schellens, Jan H.M. | Beijnen, Jos H.
Echinacea purpurea is one of the most popular herbal medicines and is known for its immunostimulatory effects. Alkylamides are the main lipophilic components of E. purpurea that contribute to its pharmacological actions. For quantification in human plasma of one of these alkylamides, undeca-2-ene-8,10-diynoic acid isobutylamide, a sensitive LC–MS/MS assay has been developed and validated. Plasma samples were pretreated using liquid–liquid extraction with a mixture of diethyl ether and n-hexane (50:50, v/v). Dried extracts were reconstituted in 50μL of acetonitrile–water (50:50, v/v) after which 15μL of sample was injected into the HPLC system. HPLC was performed using a Polaris 3 C18-A column (50mm×2mm ID) and isocratic elution with acetonitrile–water (50:50, v/v) containing 0.1% formic acid at a flow rate of 0.3mL/min. Subsequently, electrospray ionization in the positive ion mode followed by tandem mass spectrometry was performed for detection. The total run time was 3min. The assay was validated over a concentration range from 0.05 to 50ng/mL for undeca-2-ene-8,10-diynoic acid isobutylamide, with 0.05ng/mL being the lower limit of quantification using 1.0mL plasma samples. Inter-assay inaccuracy (±12.7%), within-day and between-day precisions (CV≤8.23%) were acceptable. Further, undeca-2-ene-8,10-diynoic acid isobutylamide was found to be chemically stable under relevant conditions. Finally, the applicability of this assay has been successfully demonstrated in a pharmacokinetic experiment in which a human volunteer ingested a commercial extract of E. purpurea.
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