Determination of Fe upon Special "Upconversion Luminescence" of Dopamine.

A promising technique based on the luminescence with long wavelength excitation and short wavelength emission (LExL, λ > λ) is developed. This LExL is different from traditional upconversion luminescence (UCL). The LExL, namely, special "UCL", is realized by a xenon light source of a common spectrofluorometer. In this work, we found that dopamine (DA) has this LExL phenomenon. The LExL of DA is mainly caused by the excitations of second-order diffraction light (λ/2). The two-photon absorption properties of DA have been calculated employing the density functional response theory. The LExL and Stokes luminescence (SL, λ < λ) of DA both showed static quenching upon the addition of Fe. Dual-mode luminescence methods upon LExL (λ/λ at 565/317 nm) and SL (λ/λ at 282/317 nm) of DA were applied for the selective determination of Fe. The detection limits are 0.30 and 0.52 μmol L for LExL and SL, respectively. In addition, their linear ranges for Fe determination are both from 0.70 to 30 μmol L. The LExL method of DA not only meets the basic determination criteria for Fe but also offers additional advantages in resisting more interferences and shows satisfactory feasibility performances.