Photometric estimation of uranium in sea water based on extraction

Abstract

Uranium forms an intensely red coloured (λ_max=560 nm)complex with PAN,1-(2-pyridylazo)2-naphthol, at <i>p</i>H 8-10 which can be extracted quantitatively into 1,2-dichloroethane in a single extraction step. The interference of several metal ions present in sea water such as Be(ii), Mn(ii), Fe(iii), Co(ii), Ni(ii), Cu(ii), Zn(ii), Mo(Vi), Hg(ii), Th(iv), Y(iii) and lanthanides can be effectively masked by the addition of 1,2-diamino cyclohexane tetraacetic acid (CDTA).The red colour of the complex in the organic phase is fairly stable and obeys Beer's law up to 10 <i>µ</i>g of uranium/litre, the molar extinction coefficient and sensitivity of the colour reaction being 24,000 and 0.01 <i>µ</i>g cm^-2 respectively. The method has been applied for the estimation of uranium in coastal waters of Bay of Bengal around Visakhapatnam and the average concentration is found to be 3.6 <i>µ</i>g/litre with a standard deviation of 0.03. The composition of the extracted species, and the conditional stability constants of the uranium-PAN complex are evaluated. The proposed method is simple, sensitive, selective and fairly reproducible for the estimation of uranium in sea water.