Spectrophotometric determination of microamounts of thorium with thorin in the presence of cetylpyridinium chloride as surfactant in perchloric acid

A simple and more sensitive spectrophotometric method is developed for determination of thorium using thorin as a chromogenic reagent in the presence of cetylpyridinium chloride (CPC) in perchloric acid. The reaction was instantaneous and complex was found stable for 168 h. A significant bathochromic shift was noted in the presence of CPC. The determination range was enhanced from 25 to 30 μg mL^?1 with molar absorptivity of 2.95 × 104 L mol^?1 cm^?1 at 25 ± 5 °C. Sandell’s sensitivity was calculated to be 6.8 ng cm^?2 at 581 nm. Relative standard deviation was reduced from 4.25 to 2.5. The interference of Ni²⁺, Mn²⁺, Sn⁴⁺, phosphate, EDTA, sulphate and tartrate has been reduced significantly in the presence of surfactant. The validity of the proposed method was tested by determining thorium in Certified Reference Materials.