Resin column beds were pre-conditioned by passing through them 10 ml of a 2.0 mol/l HCl solution.
Then, columns were washed with 20 (Amberlite IRP-69, Dowex 50W × 8-400, Dowex HCR-W2) and 40 ml of water (Diaion WT01S).
Conditioning solutions and water were passed at a flow rate of 4.0 ml/min using a 4-channel MasterFlex L/S peristaltic pump (Cole-Parmer, Vernon Hill, IL, USA).