The mobile phase was 80% (v/v) 25 mM ammonium formate buffer (pH 3.4) and 20% (v/v) methanol.
A volume of 100 µL was injected in a HPLC column (l Bondapak 3.9 ×300 mm, RP-18 C, Waters, Division of Millipore). Flux was set at 1 mL/min and quinoxalines were detected at 320 nm.