Characterisation of Ho-DTPA and Y-DTPA complexes by capillary isotachophoresis and TLC with radiometric detection

The complexation of holmium and yttrium with DTPA (diethylentriaminepentaacetic acid) was studied as a first step for labelling of monoclonal antibodies for radiopharmaceutical application. Thin-layer chromatography (TLC) with radiometric detection was used to determine the suitable conditions for the preparation of studied complexes. The optimum pH of the reaction mixture, radionuclide:ligand ratio, reaction time and stability of selected complex compounds were found. To find out the physico-chemical properties (stability constants) of Ho-DTPA and Y-DTPA complexes the capillary isotachophoresis (cITP) with conductivity detection was applied using the fact that a good linear relationship exists between the stability constants of lanthanide-DTPA complexes and the zone reduction due to the bleeding effect (liberation of free metal ion). Satisfactory agreement between the stability constant values of Ho-DTPA and Y-DTPA complexes determined by ITP and ones obtained from the SC Querry Database was obtained.