Photometric Determination of Micro Amounts of Thorium in Marine Products with a New Chromogenic Reagent Dibromo-o-carboxy Carboxyarsenazo

A new chromogenic reagent,2-(3′,5′-dibromo-2′-carboxyphenylazo)-7-(2″-arsono-5″-carboxyphenylazo)-1,8-dihycroxy-3,6-naphthalene disulfonic acid (abbreviated as CAsA-DBC) was synthesized with a yield of 74%.It was found that a blue colored coordination complex of Th(Ⅳ) and CAsA-DBC with mole ratio of amount of substance 1∶2 was formed in HCl (1+19) solution.Absorption maximum of the complex was found at the wavelength of 640 nm,where the value of apparent molar absorptivity was found to be 1.11×105L·mol-1·cm-1.Beer′s law was kept in the range within 20 μg of Th(Ⅳ) per 25 mL of solution,corresponding to the linear regression equation A=0.093 2 C (μg/25 mL)+0.000 5 (r=0.999 1).Macro amounts of many commonly co-existing metal ions,including the associating uranium(Ⅵ),did not interfere with the determination of thorium by this method.In the application of this method to analysis of several marine products,values of RSD′s (n=5) obtained were less than 3.1%,and values of recovery found were in the range of 99.3%-103.5%.