The experimental conditions were the following: mobile phase 0.004M sulphuric acid; isocratic
method; flow-rate 0.6ml/min; detection at 210 nm; injection volume 20 ml; HPLC column Aminex HPX-87H, 300 × 7.8 mm, 9 µm (Bio-Rad, Gladesville, Australia), column temperature: 35°C. All solvents were HPLC-grade and weredegassed before use.