electrospray
ionisation source (ESI). Separation was achieved on an Acquity
TM BEH C18 column (100 mm 2.1 mm i.d., 1.7 lm; Waters).
The detection wavelength was set at 520 nm. The mobile phase
was a mixture of 4.5% formic acid (A) and acetonitrile (B). The gradient
program was as follows: initial conditions – 99% (A), 12 min –
75% (A), 12.5 min – 100% (B), 13.5 min – 99% (A). The flow rate was
0.45 mL/min, and the injection volume was 5 lL. The column was
operated at 30 C.