Fluorescence reaction of scandium with 5-hydroxychromone and its derivatives

Scandium forms yellow complexes with 5-hydroxychromone and its derivatives, which are extracted into various organic solvents. These complexes exhibit yellow-green fluorescence which is the most intense and constant when extracted from a solution of pH > 11.0. The substituent effect of alkyl, acetyl and methoxyl groups on the fluorescence behavior was studied and compared with that in the case of beryllium complexes previously reported. Furthermore, the fluorometric determination of scandium was attempted. The substituent effect was similar to that on the beryllium complexes. The maximum wavelengths of absorption, excitation, and emission spectra were nearly 395, 400, and 505 nm, respectively, except those of the complex of 2-methyl-7-methoxy derivative, which were shifted to shorter wavelengths. The relative fluorescence intensities in benzene were increased by the introduction of alkyl group into the 2- and 3- positions, especially the 2-position, of 5-hydroxychromone. The fluorescence intensities of 2,3-dialkyl derivatives were about 14 to 15 times that of 5- hydroxychromone. Introduction of an acetyl group into the 3-position decreased the intensity. Methoxyl group in the 7-position increased the intensity. Only the effect of methoxyl group in the 7-position was different from that observed with beryllium complex. Among the derivatives examined, 2-ethyl-3-methyl-5- hydroxychromone was the mostmore » suitable reagent for the fluorometric determination of scandium, since the fluorescence of its complex was one of the most intense and stable. As an extraction solvent benzene is useful because of high stability of the complex in it. The calibration curve is linear up to 4.0 mu g of scandium. The effects of diverse ions were examined. (auth)« less