Phosphinimines as selective extractants for Tc-99 pertechnetate

The triphenylphosphiniminium cation (Ph 3 P=NH 2 + ) was evaluated for its selectivity for the pertechnetate anion ( 99 TcO 4 − ) using both solvent extraction and solid phase extraction methods. The solid phase extraction of TcO 4 − using trimethylsilyl-protected triphenylphosphinimine coated silica gel demonstrated the selectivity of the triphenylphosphiniminium cation for TcO 4 − over a variety of inorganic (NO 3 − , Cl − , H 2 PO 4 − , HSO 4 − /SO 4 2− ) and organic (fumarate) anions in aqueous solution (>98% extracted when at pM TcO 4 − vs. 0.15 M anion). Iodide, lactate, benzoate and acetate were able to compete with pertechnetate (only 11–83% extracted) when present in large excess (0.15 M anion vs. 10 −12 M 99m TcO 4 − ), but not when the anion was present in a 10-fold excess. The triphenylphosphiniminium cation was significantly selective for TcO 4 − over ReO 4 − , a commonly used non-radioactive analog for 99 Tc, when tracer amounts of both competed with the anions iodide, lactate, benzoate and acetate.