The separation was performed on a 5 lm ZORBAX
SB-C18 column (150 9 4.6 mm i.d.) under isocratic
conditions with a mobile phase composed of acetonitrile-
10 mM aqueous sodium acetate (7:93 v/v). Analyses were
performed at room temperature under a flow rate of 1 ml/
min using an injection volume of 100 ll.