A New Spectrophotometric Method for Thorium Determination Using 1,4-Dihydroxyanthraquinone

A new reagent, 1,4-dihydroxyanthraquinone (1,4-DHA), is described for the spectrophotometric determination of thorium(IV). Optimization of the formed thorium−1,4-DHA complex was performed by studying several parameters such as methanol concentration, suitable pH, dye concentration, temporal stability of the formed complex and thorium concentration (calibration curve). The optimized method was applied to different rock types bearing thorium with good accuracy results. This reagent is highly sensitive toward thorium; thorium complex has a molar absorptivity of 1.82 × 104 L/(mol cm) at 600 nm and pH 3.25. Beer’s law was obeyed in the range from 0.9 to 20 µg/mL for Th(IV). The tolerance limits for several metal ions were calculated and gave high tolerance limit especially for uranium. Details are given for the estimation of thorium in standard reference and natural rocks.