A new liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the determination of five flavonoids including scutellarin, naringenin, apigenin, luteoline and wogonin in rat plasma using sulfamethalazole as internal standard (IS). Plasma samples were pretreated with liquid-liquid extraction procedure and acid hydrolysis method was used for converting conjugated flavonoids to their respective free forms. The chromatographic separation was performed on a C(18) column with a linear gradient elution using a mobile phase consisted of 0.01% acetic acid and methanol. The detection was accomplished by multiple-reaction monitoring (MRM) scanning with electrospray ionization (ESI) source operating in the negative ionization mode. The optimized mass transition ion-pairs (m/z) monitored for scutellarin, naringenin, apigenin, luteoline, wogonin and IS were 461.1/285.1, 271.0/119.0, 269.0/117.0, 285.0/132.9, 283.0/268.0 and 252.0/155.9, respectively. The method was linear for all analytes over investigated ranges with all correlation coefficients greater than 0.9915. The lower limit of quantitation (LLOQ) of scutellarin was 9.15 ng/mL and other compounds were all less than 2.0 ng/mL. The proposed method showed appropriate accuracy and repeatability and was suitable for pharmacokinetic studies of the five flavonoids after oral administration of Scutellaria Barbata extract.
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