Metal ion interferences in reverse polarity capillary zone electrophoretic analysis of Hanford Defense Waste for ethylenediaminetetraacetic acid (EDTA) and n-hydroxyethylethylenediaminetriacetic acid (HEDTA) Original Research Article

Chemical characterization of Hanford Defense Waste (HDW), which was accumulated during the processing of irradiated reactor fuels for nuclear weapon production continues to be a challenging analytical problem. Complexants in particular are difficult to analyze because in their free state, they are highly polar, exhibit low volatility, and exist in several charge states. In addition, they form complexes with metal ions resulting in multiple species. Analysis is also difficult because HDW is high in radioactivity, high in ionic strength, and high in hydroxide concentration. This account describes the first application of reverse polarity capillary zone electrophoresis (RPCE) for the determination of EDTA and HEDTA in HDW. In this report, RPCE parameters for a rapid separation of uncomplexed EDTA and HEDTA in aqueous solution were established. The buffer containing 25 mM borate and 25 mM hexamethonium bromide (HMB), an electroosmotic flow modifier, at pH 9.2, effectively separated EDTA and HEDTA in less than 6 min when −20 kV was applied across a 50 μm i.d. × 50 cm long bare capillary column. The separation of metal complexes of EDTA and HEDTA was achieved using an electrolyte of higher buffer capacity containing 25 mM borate/25 mM boric acid/25 mM hexamethonium bromide in aqueous basic solution. The stability of metal EDTA and HEDTA complexes in Synthetic Hanford Waste (SHW), a simulant for HDW, was tested for Bi3+, Ca2+, Cu2+,Cd2+, Cr3+, Cr2O72−, Hg2+, UO22+, Ni2+, Fe3+, and Th4+ under basic conditions. It was observed that the metal complexes were unstable under the harsh conditions of SHW. Only Pb2+ formed stable EDTA and HEDTA complexes in SHW. Preliminary data from the analysis of real HDW samples by adding Pb2+ in basic citrate solution demonstrated the potential of RPCE for the determination of total EDTA and HEDTA in real samples.