The use of formamidine sulphinic acid as a reducing agent in the presence of technetium-99-pertechnetate and diethyldithiocarbamate ligand has been shown to yield a complex containing a Tc = CO bond. The carbon monoxide present in this complex originates from the reducing agent itself. Evidence is presented which suggests that this carbonyl complex is present in the 99mTc-diethyldithiocarbamate preparation obtained by the use of formamidine sulphinic acid as the reducing agent. Use of hydrazine as a reducing agent yields a complex containing a Tc = N bond. It is apparent that when reducing agents such as hydrazine or formamidine sulphinic acid are used in the preparation of 99mTc-radiopharmaceuticals, the possibility of the formation of complexes structurally different to those obtained by the use of stannous chloride must be considered.
