Bathophenanthrolinedisulfonic acid, disodium salt is a water-soluble derivative of Bathophenanthroline. It is insoluble in organic solvents. Its pKa1 and pKa2 are 2.83 and 5.20, respectively. Due to its high water solubility, Bathophenanthrolinedisulfonic acid can be used to detect Fe(II) in aqueous samples such as blood or biological fluids. The detection range of Fe2+ using Bathophenanthrolinedisulfonic acid is 0.25-4 ppm at 535 nm. The molar absorptivity of the complex is 2.24×104. The reduction and oxidation potential of FeL3 2+-FeL3 3+ in 1 M H2SO4 solution is reported to be 1.09 V. Cu+ can also be detected using Bathophenanthrolinedisulfonic acid. The maximum wavelength and molar absorptivity of the Cu+ complex is 483 nm and 1.23×104, respectively.
1. D. Blair, et al., Bathophenanthrolinedisulphonic Acid and Bathocuproinedisulphonic Acid, Water Soluble Reagents for Iron and Copper. Talanta. 1961;7:163-174