Development and validation of a ultra high performance liquid chromatography-tandem mass spectrometric method for the direct detection of formoterol in human urine

Formoterol is a long acting β2-agonist and has proven to be a very effective bronchodilating agent. Hence it is frequently applied therapeutically for the treatment of asthma. Because β2-agonists might be misused in sports for the stimulatory effects and for growth-promoting action their use is restricted. Since January 2012, formoterol is prohibited in urinary concentrations higher than 30 ng/mL. The objective of this study was to develop and validate a simple and robust ultra high performance liquid chromatographic-tandem mass spectrometric (UHPLC-MS/MS) method for the direct quantification of formoterol in urine. Sample preparation was limited to an enzymatic hydrolysis step after which 2 μL was injected in the chromatographic system. Chromatography was performed on a C8-column using gradient conditions. The mobile phase consisted of water/methanol (H2O/MeOH) both containing 0.1% acetic acid (HOAc) and 1 mM ammonium acetate (NH4OAc). Calibration curve were constructed between 15 and 60 ng/mL. Validation data showed bias of 1.3% and imprecision of 5.4% at the threshold. Ion suppression/enhancement never exceeded 7%. Calculating measurement uncertainty showed proof of applicability of the method. Stability of formoterol was also investigated at 56 °C (accelerated stability test) at pH 1.0/5.2/7.0 and 9.5. At the physiological pH values of 5.2 and 7.0, formoterol showed good stability. At pH 1.0 and 9.5 significant degradation was observed.