Calcein Blue is a fluorescent metal indicator in EDTA titration. It is highly soluble in alkaline solutions, but slightly soluble in water. Its proton dissociation constants are reported to be pKa1=2.45, pKa2=7.24 and pKa3=11.3. Calcein Blue solution emits bright blue fluorescence (λem=445 nm) at pH 4-11, but no fluorescence at pH 12 or higher. The blue fluorescence of the Calcein Blue solution at pH 4-11 is quenched by metal ions such as Co, Cu, Mn, Ni, and Pb. However, Calcein Blue forms a highly fluorescent complex with alkaline earth metals at pH 12 or higher. Since the endpoint of the chelate titration is clear by UV irradiation at 200-370 nm in a dark room, highly stained samples can be used. Calcein Blue is also suitable to determine Fe and Zr ions. Calcein Blue-Zn chelate can detect 10 ppb of F-. Calcein Blue aqueous solution emits laser at 449-490 nm.
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