Development and validation of a UPLC‐ESI‐MS/MS method for the determination of N‐butylscopolamine in human plasma: Application to a bioequivalence study

A sensitive and fast ultra performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) method for measurements of N-butylscopolamine in plasma was developed and validated. A single protein precipitation was proposed for the clean up of the plasma and N-methylhomatropine was added as internal standard (IS). The analyses were carried out using a C(18) column and mobile phase of acetonitrile: 5 mM ammonium acetate + 0.1% formic acid (90:10, v/v). The triple quadrupole mass spectrometer equipped with an electrospray source in positive mode, was set up in selective reaction monitoring, to detect precursor → product ion 360.0 → 194.0 m/z and 290.3 → 138.0 m/z transitions, for N-butylscopolamine and IS, respectively. The method was linear in 0.03 (lower limit of quantitation; LLOQ) - 10.00 ng/ml range for N-butylscopolamine. Satisfactory selectivity, linearity, precision, accuracy, and robustness were obtained for the UPLC-ESI-MS/MS method. The proposed method was successfully applied to a pharmacokinetic study of healthy human volunteers; the results showed that the two scopolamine butylbromide formulations tested are not bioequivalent in rate and extent of absorption.