Determination of trace thorium in fly ash by catalytic spectrophotometry

Trace Th(IV) catalyzes strongly decolorization reaction of picraminicazochromotropic acid(PAACA) by oxidizing with H2O2 in pH 2.0 HNO3 solution, the addition of emulsor OP can further increase the sensitivity of the reaction and its catalytic extent is linear with the contents of Th(IV). Based on this study, a catalysis spectrophotometric method for determining trace Th(IV) was developed. The results show that the maximun absorption of the color solution is at 545 nm and the detection limits of the method is 0.80 mug/L for Th(IV). Beer's law is obeyed for Th(IV) in the range of 4.0 similar to 120 mug/L, and the recovery of standard addition of Th(IV) is 98.5% similar to 103.6%. Combined with 1-phenyl-3-methyl-benzoylpyrazolone-6-toluene extraction, the method has been applied to the determination of trace Th in fly ash with satisfactory results.