Abstract: DERIVATIVE SPECTRA AND SIMULTANEOUS DETERMINATION OF U( Ⅳ),U(Ⅵ) AND Pu(Ⅲ)IN NITRIC ACID SOLUTION Ye Guoan;Zhao Yanju;Zhuang Weixin(China Institute of Atomic Energy,P.O. Box 275 (26),Beijing 102413)Abstract:The second derivative spectra(2nd DS)of U(Ⅳ),U(Ⅵ)and Pu(Ⅲ) in nitric acid solution is investigated and compared with each species' absorption spectra (AS). The influences of HNO_3,H~+ and other impurities on 2nd DS and AS of these species are discussed. Wide and intensive absorption band can be declined by derivation, On the other hand, weak but sharp absorption band can be amplified by derivation. U(Ⅳ) causes serious interference on absorption spectra of U(Ⅵ) and Pu(Ⅲ)if the concentration of U(Ⅳ) is higher than the concentrations of U(Ⅵ) and Pu(Ⅲ).But in 2nd DS, he characteristic peaks of U(Ⅵ) and Pu(Ⅲ) can be easily discerned and U(Ⅳ)slightly affects their determinations. The height of negative peak at 415nm can be used to determine U(Ⅵ) concentration. Either the negative peak at 584nm or the positive peak at 665nm can be used to determine Pu(Ⅲ)concentration depending on concrete situation, The determina tion of U(Ⅳ)is scarcely affected by Pu(Ⅲ) and U(Ⅵ),and its concentration can be determined via several peaksl height.2.5-3.0 mol/l HNO_3 is suitable for the determination with the analy-sis deviation below 5.0%. The low-limits of determination for Pu(Ⅲ),U(Ⅳ) and U(Ⅵ)are 0.5,0.1 and lmmol/l, respectively.Keywords: Second derivative spectra Molar absorptivity U(Ⅳ) U(Ⅵ) Pu(Ⅲ)