All supernatants were pooled and passed through
a SPE cartridge, Strata SCX (55 lm, 70 Å, 500 mg/3 mL) (Phenomenex,
Cheshire, UK), following preconditioning of the cartridge with
distilled water. 5 mL of the cartridge eluate was analysed in triplicate
by HPLC with photodiode array, fluorescence and mass spectrometric
detection (HPLC–PDA–FL–MS2).