[en] The work described in this paper is part of a leaching study being conducted for the Battelle Pacific Northwest Laboratory's Waste Isolation Safety Assessment Program. Simulated high-level reactor waste glass was leached with three solutions, one of which was a saturated-salt brine. Because chemical separation of Np and Pu using organic extraction or anionic exchange is not effective for the brine samples, a procedure has been developed to first separate neptunium and plutonium from high concentrations of brine before proceeding with an extraction of neptunium from plutonium. Samples were equilibrated with tracers, Np and Pu were co-precipitated with La(OH)₃, and interfering ions were removed by washing the hydroxide precipitate with water. Pu and Np were separated by reducing Pu to Pu³⁺ and extracting the Np⁴⁺ into thenoyltrifluoroacetone; control of oxidation states and contaminant concentration is critical