Quantification of tulobuterol, a selective β2 adrenergic agonist, in human plasma by liquid chromatography-tandem quadrupole mass spectrometry

A simple and highly sensitive method coupled with liquid chromatography-tandem quadrupole mass spectrometry （LC-MS/MS） was developed and validated for the determination of tulobuterol in human plasma. Sample was preparated by liquid-liquid extraction with i-propanol-n-hexanc （5：95, v/v）. Tulobuterol and tulobuterol-d9 （internal standard, IS） were separated on a 300 Extend Cls column （4.6 mm~150 mm, 5 ~tm）, using 0.1% formic acid （A）-acetonitrile （B） （30：70, v/v） as the mobile phase at the flow rate of 1.0 mL/min with an approximately 1：1 split entering the mass spectrometer. Detection was performed by positive electrospray ionization mass spectrometry multiple reaction monitoring of the precursor-to-product ion transition of tulobuterol at m/z 228.1→m/z 154.0 and tulobuterol-d9 at m/z 237.2→m/z 154.0. The assay was linear over the range 0.0l-5.0 ng/mL with a lower limit of quantitation of 0.01 ng/mL. The intra- and inter-day precisions were 3.7% and 11.1%, respectively. Recovery was approximately 66%, and matrix effects were minimal. This method also showed satisfactory sensitivity, specificity, and carryover. The method was successfully applied to a pharmacokinetic study of tulobuterol in healthy volunteers who were given the tulobuterol patch containing 2 mg tulobuterol.