Five milliliters of 6 M HCl was added to each
extract to give a 25 mL solution of 1.2 M HCl in 50% aqueous
methanol. Extracts were refluxed at 90 °C for 2 h, cooled, and
centrifuged for 15 min at 2000g in a Sorval centrifuge (model
RC-5B, DuPont Instruments). Supernatant was taken and
filtered through a 0.45 ím filter prior to analysis of 20 íL by
reversed phase HPLC.