Ferric Ion Complexes Other chemical methods based on the oxidation of
ferrous ion (Fe2þ) to ferric ion (Fe3þ) in an acidic medium and the formation of
iron complexes have also been widely accepted. These methods spectrophotometrically
measure the ability of lipid hydroperoxides to oxidize ferrous ions to ferric
ions, which are complexed by either thiocyanate or xylenol orange (23, 28, 29).
Ferric thiocyanate is a red-violet complex that shows strong absorption at 500–
510 nm (8). The method of determining PV by coloremetric detection of ferric thiocyanate
is simple, reproducible, and more sensitive than the standard iodometric
assay, and has been used to measure lipid oxidation in milk products, fats, oils,
and liposomes (8, 23).