Bound Iron and Unsaturated Iron-binding Capacity of Serum;Rapid and Reliable Quantitative Determination

Abstract

Summary

1. New, rapid, and reliable methods for determination of siderophilin-bound iron and of iron-free siderophilin in small amounts of sera or plasma have been devised. 2. Bound serum iron is determined by adjustment of serum sample with concentrated phosphate buffer to a pH value at which constituent proteins remain in solution but siderophilin-bound iron is wholly dissociated and available to combine with a suitable chromo-genic agent, (terpyridine). Ascorbic acid is used as the iron reductant. Iron-terpyridine complex in treated serum is measured by light absorption of a test solution at 552 mμ against a treated serum control minus terpyridine. A standard iron-terpyridine curve permits ready estimation of amount of iron in original serum sample. 3. The proposed method for determination of iron-free siderophilin, or unsaturated iron-binding capacity of serum (UIBC), involves addition to serum of iron in excess of that capable of being bound, followed by direct analysis of serum sample with terpyridine as the chromogenic agent without acidification or the removal of constituent proteins. A serum control to which the same amount of iron but no terpyridine is added furnishes the necessary correction for the absorption at 552 mμ of iron-siderophilin complex in the rest sample. The difference between quantity of iron added to serum and that found to be in excess is equal to the UIBC.