Abstract
Coloration reaction of 2', 3', 6', 7'-tetrahydroxyfluoran derivatives with metal ions is bathochromic and examination was made on the use of these compounds as an indicator of metal ions like Pb, Hg, Bi, Ce, La, Cd, Co, Ni, Cu, Mg, Ca, and Ba chelate titration with 2', 3', 6', 7'- and 1', 3', 6', 8'-tetrahydroxyfluoran derivatives as indicators was carried out using metal solutions of pH 3∼4 (ammonium acetate buffer), over pH 3 (dil. HNO3), pH 4∼6 (hexamine buffer), pH 10 (NH4OH·NH4Cl buffer), over pH 10 (NH4OH soln.), and above pH 10 (NaOH soln.). The halogen derivatives (Cl, Br, I) of 3', 6', 7'- and 3', 6', 8'-trihydroxyfluoran derivatives effected clearer color change by titration due to the auxochromic effect of the halogen atom, and sensitivity of the color increased in the order of Br, Cl, and I, and the positions if the substituted halogens and hydroxyl also affected sensitivity to coloration, sensitivity decreasing in the order of 4'-, 2'-, 2', 4'- halogeno-3', 6', 7'- and 2', 4'-, and 2', 4'-halogeno-3', 6', 8'-trihydroxyfluoran derivatives. In the hydroxyfluoran-complexone compound, bathochromic coloration occurred in the increasing order of 2', 3', 6', 7'-hydroxyfluoran-imindiacetic acid, aminoacetic acid-complexone, and hydroxyfluoran.
