Spectrofluorimetric determination of trace amounts of thorium

A spectrofluorimetric method, based on the formation of a fluorescent complex with salicyladehyde carbohydrazone, is optimized for the determination of thorium (20–800 μg l^?1) at “pH” 1.3–1.7. The relative standard deviation is 2.7% for 100 μg Th l^?1. The method is applied to synthetic mixtures containing various amounts of thorium and to the determination of thorium in monazite samples.