A cloud point extraction process using mixed micelle of the cationic surfactant
CTAB and non-ionic surfactant Triton X-100 to extract thorium(IV) from aqueous
solutions was investigated. The method is based on the color reaction of thorium
with 5-(2`,4`-dimethylphenylazo)-6-hydroxypyrimidine-2,4-dione (DMPAHPD) in
the presence of potassium iodide in hexamethylenetetramine buffer media and mixed
micelle-mediated extraction of complex. The optimal extraction and reaction
conditions (e.g. surfactant concentration, reagent concentration, effect of time) were
studied and the analytical characteristics of the method (e.g. limit of detection, linear
range, molar absorptivity, Sandell sensitivity, preconcentration, and improvement
factors) were obtained. Linearity was obeyed in the range of 0.5–15 ng mL−1 of
thorium(IV) ion and the detection limit of the method is 0.16 ng mL−1. The
interference effect of some anions and cations was also tested. The proposed method
was successfully applied for the preconcentration of trace thorium in natural water
samples as well as in plant material and soil samples prior to its determination by
inductively coupled plasma atomic emission spectrometry (ICP-AES) with
satisfactory results.