5-(2'-CARBOXYPHENYL)AZO-8-QUINOLINOL AS A SENSITIVE REAGENT FOR EXTRACTIVE SPECTROPHOTOMETRIC DETERMINATION OF URANIUM IN GEOLOGICAL SAMPLES

A new sensitive extractive spectrophotometric method has been suggested for the determination of uranium in soils, stream sediments and rock samples using 5-(2'-carboxyphenyl)azo-8-quinolinol (R). Uranyl nitrate is extracted in isobutylmethyl ketone (MIBK) at pH 5.2-6.1 in presence of saturated ammonium nitrate solution. The aqueous solution of R is shaken with MIBK containing uranyl nitrate. R forms almost instantaneously an amber coloured complex with the uranium in MIBK. The complex is stable for 24 hours. The molar absorptivity and Sandell's sensitivity of the complex are 1.035 . 10(4)l . mol(-1). cm(-1) and 0.022 mu g . cm(-2), respectively, at lambda(max) 524 nm. Beer's law is obeyed over the range 1.4-7.1 mu g . ml(-1) of uranium. An amount as low as 1.4 mu g . ml(-1) of the uranium could be satisfactorily determined within a relative standard deviation of +/- 1.7%. The proposed method is sensitive, highly precise, simple in operation, rapid and reliable.