A new and advantageous extraction procedure was developed for extraction of cerium (IV) from nitric acid with di-n-butylsulfoxide (DBSO) in perchloric acid. The extracted Ce (IV) was determined spectrophotometrically using 0.01 % solution of arsenazo-III in 3 M per-chloric acid. Various parameters such as equilibration time, metal ion concentration, effect of temperature and diverse ions on the extraction of the Ce (IV) were established. U (VI), Th (IV) and Pb (II) interfere whereas only

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... te and fluoride suppress the extraction among anions. The stoichiometric composition of the cerium complex with DBSO was determined by slope analysis and found to be 1:4. The process of extraction was found to be exothermic. Deionized water was the most appropriate solvent for back extraction of cerium. This method is easier and more sensitive than many of the reported procedures. KEYWORDS Cerium, extraction, DBSO, perchloric acid, arsenazo-II. Experimental Reagents, Solutions and Apparatus All chemicals used were of analytical grade. Cerium sulphate stock solution (1000 µg mL -1 ) was prepared in 2 M sulphuric acid. Solutions of arsenazo-III were prepared by dissolving the measured amount of disodium salt of the compound in HClO 4 . Salting-out agent solution (0.01 molar) was prepared by adding 3.75 g of Al(NO) 3 .9H 2 O in deionized water and further dilutions were made to prepare solutions of required concentrations. Potassium phosphate, potassium fluoride, sodium sulphate, sodium cyanide, sodium chloride and sodium thiosulphate solutions were made by adding 100 mg of each salt in deionized water and making up the total volume to 10 mL. Uranyl nitrate, thorium nitrate, zinc chloride, lead nitrate solutions were made by adding 100 mg of respective salt in deionized water and making up the total volume of 10 mL. 7.5 M nitric acid solution was made by taking 425 mL (15.7 M) nitric acid and diluting it to