A spectrophotometric study of the thorium-morin mixed-color system

Abstract

Thorium reacts with morin in solutions at a pH of 2.0 to yield a single complex that has a thorium:morin ratio of 1:2. The yellow complex has a maximum absorbance at 410 m and is stable for at least 7 hours. The sensitivity of the reaction is such that as little as about 0.2 microgram of ThO 2 in 50 ml can be determined using a light path of 5 cm. An average apparent equilibrium constant of approximately l x 10 6 was found for the reaction. The effects of acidity, alcohol content, morin content, time, age of the morin reagent and temperature of the reaction have been studied as have the effect of some other ions. Zirconium and aluminum interfere seriously and must be absent. The interference from ferric iron is also serious but the effect may be appreciably decreased if hydroxylamine is added to the solution. Relatively large amounts of calcium and lanthanum may be present without causing interference, and these ions can be used as carriers in separations of thorium from other ions. Morin is a suitable reagent for the determination of thorium in pure solutions. If appropriate separations are found for the separation of thorium from other ions, the reaction will be useful for the determination of trace amounts of thorium in complex materials. The information presented in this paper is fundamental to any specific adaptation of the reaction to the analysis of complex materials.