Triple quadrupole mass spectrometry

A Triple Quadrupole Mass spectrometry (Waters, Micromass UK Limited) equipped with an electrospray ionization (ESI) interface operated with Masslynx 4.1 software was used. The MS detection was performed in both positive (+ ve) and negative (− ve) ion modes to capture the strongest ion. All compounds were first analysed individually in syringe infusion condition with a flow rate of 5µL/min. Optimization of parameters of the MS method was obtained by entering the molecular ion masses into the massLynx software. The default ranges for cone voltage and collision energy were used to enable MassLynx software to automatically determine all other parameters, such as capillary voltage, desolvation temperature, gas flows and Multiple Reaction Monitoring (MRM) transitions. Nitrogen and argon gases were used as nebulizing and collision gases respectively. The ion source parameters were capillary 3.2 kV; exit potential 3 V; radio frequency (RF) lens 0.2 V; source temperature 110 °C; and desolvation temperature 400 °C. The desolvation and cone gas flow were 650 and 130 L/hr. Product ions and corresponding collision energies were stored in the method files. The two most intense MRM transitions were selected for quantification and qualification except ibuprofen, of which one precursor ion was observed because of the very low intensity of the second product ion.