Determination of iron limiting values according to PH. EUR. using 1,3-dibromo-5,5-dimethylhydantoin (DBH) instead of elemental bromine. Analytical methods of pharmacopoeias with DBH in respect to environmental and economical concern. Part 8.

PH. EUR. 2002 uses elemental bromine performing iron limit tests for maleic acid (iron 5 ppm) and titanium dioxide (iron 200 ppm). 1,3-Dibromo-5,5-dimethylhydantoin (DBH) can replace bromine water. For the iron limit test of maleic acid bivalent iron is oxidized to trivalent iron by bromine resp. DBH, because the unsaturated, in high concentration existing acid reacts substantially slower. On the other hand maleic acid removes the excess of bromine. The bromine oxidation for the iron limiting values of titanium dioxide according to the pharmacopoeia is not required. Metallic iron as well as ferrous salts are converted to trivalent iron, when the titanium test solution is prepared by boiling with concentrated sulphuric acid in the presence of anhydrous sodium sulphate.