Analytical HPLC analyses were carried out with an Agilent 1200 series system equipped with an Agilent DAD detector using a Phenomenex (Aschaffenburg, Germany) reversed phase Kinetex EVO C18 column (250 × 4.6 mm). Samples were analyzed at two wavelengths (λ = 260 nm, 307 nm) at 25 °C and a flow rate of 1 mL min -1 . Isocratic elution was performed using 97% 20 mM ammonium acetate buffer and 3% acetonitrile for 7 min followed by a linear gradient to 60% 20 mM ammonium acetate buffer and 40% acetonitrile over 8 min. Afterwards, the initial conditions were restored and maintained for 4 min.