and residual Fe-
EDTA in the supernatant was determined by ionexchange
chromatography using an ODP-50 column
(4.6 · 250 mm, Shiseido) attached to a Capcell C18
UG120 guard column. Elution was carried out by
passing 20 mM phosphate buffer containing 10 mM
tetrabutyl ammonium at a flow rate of 0.8 ml/min.
After dilution with 20 ppm ferric nitrate solution
(·500), followed by filtration through a 0.45-lm