As metallofluorescent indicators, 2-naphthylamine-N, N-diacetic acid (I), 8-sulfo-2-naphthylamine-
N,
N-diacetic acid (II), and 7-sulfo-2-naphthylamine-N, N-diacetic acid (III) were studied.
Synthesis and purification of these compounds were easy, comparing with those of
N, N, N', N'-tetra (carboxymethyl) dianisidine (Anisidine blue
®), and they were stable in an alkaline solution. Acid dissociation constants of ligand [-N (CH
2COOH)
2] were determined by potentiometric method. p
Ka1 (carboxyl) and p
Ka2 (ammonium) were 2.35 and 5.02 for I, 2.85 and 5.31 for II, 2.69 and 5.06 for III, respectively. Fluorescences of these reagents were quenched by copper (II), cobalt (II), and nickel (II), at pH 4.5-5.5, and copper (II) showed this effect more clearing than the others. Constitution of the copper (II) complexes were 1: 1. Stability constants of these copper (II) complexes which were determined potentiometrically, were 5.8 for II and 5.2 for III logarithmically. Stability constant of complex with I was not determined because ofthe insolubility.
By using these compounds as the indicators, fluorophotometric titration of copper (H)(0.64mg) with 0.01 M ethylenediaminetetraacetic acid (EDTA) yielded good recovery. But those of nickel (II) and cobalt (II) were not available because fluorescence was not shown up by EDTA on nickel (II) and end-point was not clear on cobalt (II).
II is a good indicator in fluorophotometric titration of copper (II) with EDTA, because it is stable in an aqueous solution and has shown stronger fluorescence than I and II.
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