The HPLC system for HPLC/ESMS and HPLC/ICPMS/ESMS analyses consisted of a cation-exchange column IonoSpher C (100 × 3 mm, particle size 5 μm; Varian, Darmstadt, Germany); for optimizing chromatographic conditions, ammonium formate (5–50 mM) and pyridine (1–10 mM) buffer solutions all at pH 2.50 (pH adjusted with formic acid); and the addition of methanol (1–10%, v/v) were tested.