Extraction spectrophotometric method for the determination of trace thorium using 8-hydroxyquinoline and ethyl violet

A new highly sensitive colour system for thorium is developed. An association complex of thorium ion is formed with 8-hydroxyquinoline and ethyl violet having absorption maximum at 607 nm. The complex can be extracted into 10 ml of a mixture of benzene and MIBK (3:1) in 1 min. Its apparent ε value is 7.5 x 105 l·mol-1·cm-1 at 607 nm. Optimum conditions for the extraction have been found to be 3.5 x 10-3 mol/l sulfuric acid, 0.020 mol/l 8-hydroxyquinoline and 0.018% ethyl violet. Berr's law is obeyed for 0-4.5 μg of thorium per 10 ml. The colour of the extract is stable in 110 minutes at room temperature. The effects of 32 foreign ions and 4 complex reagents on the determination are discussed