Spectrophotometric determination of thorium with xylenol orange and cetyltrimethylammonium bromide

The thorium-Xylenol Orange reaction sensitized by cetyltrimethylammonium bromide (epsilon = 5.51 x 104 l.mole-1. cm-1) is accompanied by a bathochromic shift from 570 to 600 nm. The system is more selective than the binary system, because the reaction pH is lowered from 4.0 to 2.5; Beer's law is obeyed for 0.04 to 4.00 ppm of thorium. (author)