Determination of tulobuterol in rat plasma using a liquid chromatography–tandem mass spectrometry method and its application to a pharmacokinetic study of tulobuterol patch

• A sensitive and accurate LC–MS/MS method has been developed.
• The linearity among three doses of tulobuterol patch was analyzed for the first time.
• The range of detection (0.5–100 ng/ml) is the widest so far.

A sensitive and accurate liquid chromatography–tandem mass spectrometry (LC–MS/MS) method has been developed and validated for determination of tulobuterol in rat plasma for the first time. Plasma samples were extracted by liquid–liquid extraction method with methyl tert-butyl ether and the analyte and clenbuterol (IS) were separated on a Venusil MP C18 column (100 mm × 2.1 mm, 3 μm) using 0.1% formic acid–water–methanol as mobile phase, with a runtime of 5 min. The analyte was detected in multiple reaction monitoring (MRM) mode with positive electrospray ionization. Transitions of m/z 228.2 → 154.0 for tulobuterol and m/z 277.1 → 203.0 for the clenbuterol were monitored. The linear range was 0.5–100 ng/ml (r = 0.9967) for tulobuterol with the lower limit of quantitation of 0.5 ng/ml. The intra-day and inter-day precisions were less than 10.3% for the analyte and the accuracy was less than −8.6%. The RSD of matrix effect and recovery yield were within ±15% of nominal concentrations and tulobuterol was stable during stability studies. The validated method has been successfully applied to a pharmacokinetic study of three doses of tulobuterol patch in rats for the first time.