The eluate was collected into a 1.4 cm i.d. round-bottomed glass vial and evaporated at 37◦C under a gentle flow of nitrogen. The residue was reconstituted with 500 L of methanol/water (40:60, v/v). The obtained solution was centrifuged and then 200 L of clean supernatant transferred to an autosampler vial. A 10 L aliquot of the final solution was analyzedby LC/ESI–MS/MS.