Selective Fluorimetric Determination of Trace Amounts of Cobalt(II) with the System of Fluorescein–Hydrogen Peroxide–Tiron

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Abstract
The decomposition reactions of fluorescein (Fl) or its halo derivatives in the basic region were systematically investigated in the presence of an oxidizing agent such as hydrogen peroxide and/or a metal ion such as cobalt(II) and/or catalytic agent such as tiron as an activator. Moreover, a highly selective spectrophotofluorimetric method for the determination of trace amounts of cobalt(II) was established by measuring the difference in relative fluorescence intensities (ΔF) between Fl–tiron–hydrogen peroxide and Fl–tiron–hydrogen peroxide-cobalt(II) solutions at an emission wavelength of 510 nm, with an excitation wavelength of 490 nm (the calibration graph was linear in the range of 0–6 ng cobalt(II) per 25 cm3). The applications to the assay of cobalt in cyanocobalamine (vitamin B12) preparations and its eye drops were also investigated, the results were relatively good.