To prevent the HPLC column from plugging from solids, all samples were either filtered using a 0.45 m syringe filter or centrifuged at 12,000 rpm for 10 min to remove solid particles.The column was maintained at a temperature of 60◦C with 5 mMH2SO4eluent at a flow rate of 0.6 ml/min (Parades, 2009).