Determination and Pharmacokinetic Study of Synephrine in Rat by UPLC-MS/MS After Intravenous Administration

Synephrine is the primary alkaloid found in the immature fruits of Citrus aurantium, whereas the other alkaloids are present at lower levels. Synephrine is present in the peel and the edible part of the fruit. In this work, a sensitive and selective UPLC-MS/MS method for determination of synephrine in rat plasma is developed. The UPLC-MS/MS method was validated for selectivity, linearity, accuracy, precision, recovery and stability with a total run time of 3 min. After addition of carbamazepine as an internal standard (IS), protein precipitation by acetonitrile was used to prepare samples. Chromatographic separation was achieved on a UPLC BEH C18 column (2.1 x 50 mm, 1.7 mu m) with 0.1% formic acid and acetonitrile as the mobile phase with gradient elution. An electrospray ionization source was applied and operated in positive ion mode; multiple reactions monitoring (MRM) mode was used for quantification using target fragment ions m/z 168.0 -> 107.0 for synephrine, and m/z 237.3 -> 194.3 for IS. Calibration plots were linear throughout the range 5-2500 ng/mL for synephrine in rat plasma. Mean recoveries of synephrine in rat plasma ranged from 73.4 to 76.6%. RSD of intra-day and inter-day precision were both less than 12%. The accuracy of the method was between 88.5 and 109.5%. The method was successfully applied to pharmacokinetic study of synephrine after intravenous administration in rats.