Techniques for separating americium from urine after DTPA therapy.

Recent methods have been developed at this laboratory for the analysis of different chemical forms of the same isotope excreted in the urine of a human receiving DTPA (diethylenetriaminepentaacetic acid, tri-sodium, calcium salt). While DTPA bound americium is present in urine, another fraction whose excretion rate is independent of injection of the chelating agent can be isolated. Solvent extraction of acidified urine with bis (2-ethyl hexyl) hydrogen phosphate (HDEHP) removes this “unchelated” americium from the aqueous phase although it does not interact with the DTPA bound species. After the urine is ashed, reextraction with HDEHP recovers the remaining activity from the ash. This method was developed because it is rapid and does not involve elaborate equipment. The principal advantage of the method, however, is that it measures directly the effectiveness of chelation treatment for the removal of hazardous nuclides. When the gel filtration technique was used to determine the molecular weight distribution of americium in the patient urine, results strongly suggested the presence of two separate compounds. Unfortunately, the molecular weights did not differ by a large amount, and a complete separation of peaks was impossible. However, this data combined with solvent extraction results indicate that americium exists in more than one chemical form in the urine of an individual receiving periodic DTPA treatments for removal of systemically distributed 241Am.