NiEDTA does not adsorb at
258 nm. Because NiEDTA reacts only slowly with Fe(III), it does
not form FeIIIEDTA during elution. Because the FeIIIEDTA
present in the natural sample is destroyed by the irradiation, all
the FeIIIEDTA detected was formed in the column by reaction of
the adsorbed Fe(III) and “fast-reacting” metal-EDTA complexes.
The amount of NiEDTA is calculated by the difference of total
photostable EDTA and fast-reacting EDTA.