A chromatographic technique to investigate the lability of copper complexes under steady-state conditions using high specific activity Cu-64

A novel chromatographic technique is described which has prospects for stud ying the lability of a metal complex in an aqueous system. It is based on i nteractions of metal species with an ion-exchange column under steady-state conditions. For this purpose, the column is equilibrated with the sample i tself by using has the mobile phase, With the aid of a high specific activi ty radiotracer, the characteristics of the metal species interaction with t he ion-exchange column can be visualized in a radiochromatogram. Under part icular experimental conditions, information regarding the dissociation kine tics of the metal complex can be extracted from this radiochromatogram. Err oneous results due to undesirable interactions of metal species with the ch romatographic system are prevented, since the system remains in constant ch emical equilibrium with the sample to be analyzed, The potential of this te chnique was investigated with copper complexes, using high specific activit y Cu-64 for labeling. Preliminary results obtained with four complexes (Cu- EDTA, Cu-NTA, Cu-citrate, and Cu-glycine) are discussed. For three complexe s, dissociation rate constants could be determined: (6.2 +/- 0.3) x 10(-3) s(-1) for Cu-EDTA, (1.0 +/- 0.04) x 10(-2) s(-1) for Cu-NTA, and (3.1 +/- 0 .2) x 10(-2) s(-1) for Cu-citrate. No dissociation rate constant could be d etermined for Cu-glycine owing to incompatible experimental conditions.