Thermospray Mass Spectrometry Ionization Processes Fundamental Mechanisms for Speciation, Separation and Characterization of Organic complexants in DOE Wastes Page: 1 of 2
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DOE Problems Addressed
The goal of this task is to develop analytical methodology that can be used to understand the equilibria
of organic complexants and their products in multicomponent mixtures. Knowledge generated by the
success of this project can be used to address such DOE needs as: a) determining the concentration of
organic complexants to meet waste acceptance criteria prior to disposal; b) aiding in waste treatment in
which DOE EM-50 sponsors efforts to destroy chelators prior to removal of metal contaminants; and c)
processing secondary waste streams in which chelating agents are introduced to decontaminate surfaces
prior to decommissioning radioactive equipment and facilities.
The overall objective is to develop and enhance our understanding of chemical equilibria for major
organic complexant species (chelators, chelator fragments, small organic acids and their products) in
multi-component aqueous matrices such as the mixtures of DOE stored wastes. To progress toward
this objective, organic complexants must be separated and speciated in mixutres of high ionic strength.
HPLC employing zirconia-based stationary phases is being studied in order to understand the separation
requirements for organic complexants and the products formed by complexants with metals in complex
aqueous mixtures. Separated complexant species will then be characterized using positive and negative
ion thermospray mass spectrometry (JSMS). The final goal is to develop the analytical capability
needed to define chemical concentration and equilibria for complexant species in DOE waste streams.
Research Progress and Implications
Significant progress during the past twenty-eight months of the 3-year project has been made in
understanding the effectiveness of zirconia-based stationary phases for separating complexing agents such
as nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepetaacetic acid
(DTPA), citrate and oxalate. Each of these complexing agents has been used to solubilize radioactive
metals from spent fuel rods and nuclear processing equipment, and now are components of high-level
alkaline tank waste. Other chelators being studied are ethylenediamine-N,N -diacetic acid (EDDA),
imidodiacetic acid (IDA), N-2-hydroxyethyl)ethylenediaminetriacetic acid (H EDTA) and N-(2-
hydroxyethyl imonodiacetic acid (H EIDA), which may be present as degradation products and are
potential complexers of strontium and cesium, the primary fission products found in DOE tank waste.
Separation investigation initially employed bare zirconia particles with an average diameter of 3 m as
the stationary phase in HPLC separation. The zirconia is known to have Lewis acid sites that
coordinate hard Lewis bases such as carboxylates very strongly. The stationary phase also exhibits
Brbnsted acid/base character that can provide fixed charge sites for anion or cation exchange depending
on the pH of the eluant. However, it is the coordination chemistry of zirconia that has been exploited to
separate the chelators. A variety of elution conditions were tested. Two approaches were applied. The
first used gradients of increasing hydroxide or increasing fluoride concentration to provide competing
ligand to displace the complexants. However, even at very high pH, the complexants were either
irreversibly sorbed or the band width of complexant profiles was so great that this approach was deemed
impractical. In a second approach low pH gradients or low pH buffers with a gradient of increasing
ionic strength of acetate or fluoride mere used. The rationale was that at low pH the chelators would be
partially protonated in free solution and the formation constant for the zirconium-chelator complexes
would be less favorable, allowing elution of the complexants. Results indicate that if the pH is too low or
if the fluoride concentration is greater than 10 mM, the chelators elute as a group with virtually no
retention. Even with moderate pH or fluoride gradiants, the solutes do not elute in well-formed bands,
presumably due to very slow desorption kinetics.
In contrast, work with zirconia coated with quaternized polyethyleneimine (QPEI) effected the
separation of IDA, NTA and EDTA quite well under a variety of elution conditions. The separation of
these complexants on QPEI-zirconia falls into three general groups: 1) IDA, EDDa, and HEIDA are
weakly retained; 2) NTA, EDTA, HEDTA, and DTA show moderate retention and can be separated
under a variety of eluting conditions; and 3) oxalate and citrate are strongly retained and can be eluted
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Caton, John E.; Bostick, Debra T.; Carr, Peter W. & Mabbott, Gary. Thermospray Mass Spectrometry Ionization Processes Fundamental Mechanisms for Speciation, Separation and Characterization of Organic complexants in DOE Wastes, report, June 1, 1999; Oak Ridge, Tennessee. (digital.library.unt.edu/ark:/67531/metadc786021/m1/1/: accessed September 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.