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 188ReS+ as complexed with DMSA (meso-1,2-dimercaptosuccinic acid) or citrate at pH = 4.5 was stable with regard to reoxidation for up to 40 min.
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