Electrolytic reduction of carrier-free 188Re

Electrolytic reduction of 188Re7+ as an alternative to reduction with SnCl2 for protein labeling has been investigated. The electrolysis cell consisted of an “H” type cell with a tungsten cathode and a platinum anode, and 7 M HCl as the supporting electrolyte. Reduction of 188ReO4− was conducted at 25–35 V (I = 0.05–0.5 A, current density on cathode 4 × 10−3–4 × 10−2 A·cm−2) for 15 min. Ascending paper chromatography on Whatman DE81 paper in 7 M HCl at 4°C confirmed that 75–77% of 188Re was reduced to the +5 oxidation state. Subsequent to evaporation of 7 M HCl under nitrogen, it was shown that the reduced 188Re5+ as complexed with DMSA (meso-1,2-dimercaptosuccine acid) or citrate at pH = 4.5 was stable with regard to reoxidation for up to 40 min.