ELECTROLYTIC REDUCTION OF CARRIER-FREE RE-188

Electrolytic reduction of Re-188(7+) as an alternative to reduction wi th SnCl2 for protein labeling has been investigated. The electrolysis cell consisted of an ''H'' type cell with a tungsten cathode and a pla tinum anode, and 7 M HCl as the supporting electrolyte. Reduction of ( ReO4-)-Re-188 was conducted at 25-35 V (I = 0.05-0.5 A, current densit y on cathode 4 x 10(-3)-4 x 10(-2) A cm(-2)) for 15 min. Ascending pap er chromatography on Whatman DE81 paper in 7 M HCl at 4 degrees C conf irmed that 75-77% of Re-188 was reduced to the + 5 oxidation state. Su bsequent to evaporation of 7 M HCl under nitrogen, it was shown that t he reduced Re-188(5+) as complexed with DMSA (meso-1,2-dimercaptosucci nic acid) or citrate at pH = 4.5 was stable with regard to reoxidation for up to 40 min.