Spectrophotometric determination of thulium [lll] and dioxouranium ions using 8- [arylazo] -6,7 dihydroxy - 4 - methylcoumarin derivatives

ABSTRACT

The complexes of Tm [III] and UO2 [VI] with 8-[arylazo] -6,7-dihydroxy-4-methylcoumarin derivatives were investigated spectrophotometrically. The optimum conditions for chelation, pH, sequence of addition, time, solvents and stoichiometry were critically evaluated. The studies revealed that 1 1 and 1 2 [M L] complexes were formed. The higher stability constants for Tm [III] complexes compared to those of UO2+ 2 complexes were explained in terms of the hydrolysis, steric effect and nature of bonding of both metal ions. Beer's Law was valid up to 16.89 mug/cm3 for Tm3+ complexes and 23.28 mug/cm3 for UO2+ 2 complexes. Spectrophotometric methods for the determination of Tm [III] and UO2+ 2 were presented. The methods were precise as shown by low standard deviations ranging from 0.0011 to 0.0146 and high correlation coefficient [r] ranging from 0.9965 to 0.9994. The values of molar absorptivity, epsilon [LM-1 cm-1] specific absorptivity, a [ml g-1 cm-1] and Sandell sensitivity and S [mug cm-1] indicated the method to be quite sensitive compared to recommended methods using arsenazo I and thoron. A photometric titration method using EDTA as titrant was given