Adsorption of ¹⁸⁸Re Complexes with Aminomethylenephosphonate on Hydroxyapatite

Abstract

The adsorption properties of newly developed ¹⁸⁸Re complexes with aminomethylenephosphonate (amp) (EDTMP-Ethylenediamine-N, N, N', N'-tetrakis(methylenephosphonic acid), EDBMP-Ethylenediamine-N, N'-bis(methylenephosphonic acid) and NTMP-Nitrilotris(methylenephosphonic acid)) on hydroxyapatite was investigated. The adsorption of ¹⁸⁸Re complexes was strongly affected by pH and ionic strength in a solution. The adsorption coefficient(ml/g), which is defined by the ratio of the concentration of the complex per unit weight of the hydroxy-apatite to the concentration in unit volume of the solution, increased with decreasing pH and ionic strength. These observations suggest that one of the causes of the adsorption of ¹⁸⁸Re-amp is considered to be the electrostatic forces between the negative ¹⁸⁸Re-amp complex and the positive HAP surface. The adsorption affinity of the ¹⁸⁸Re-amp complex for HAP increased in the order of ¹⁸⁸Re-EDBMP<¹⁸⁸Re-NTMP<¹⁸⁸Re-EDTMP. Furthermore, the adsorption coefficient of carrier-free ¹⁸⁸Re-EDTMP was larger than that of carrier-added one under the same conditions. From a detailed comparison of the effect of the Re carrier concentration on the adsorption coefficient of ¹⁸⁸Re-EDTMP with its structural analysis by HPLC, we concluded that the Re carrier effect on the adsorption coefficient was caused by the different distribution of the components in the ¹⁸⁸Re-EDTMP mixture between the carrier-free and the carrier-added complex.