Three chromium(III) hydrolytic oligomers (monomer, dimer, and trimer) were isolated via cation-exchange from weakly acidic solutions, and their structures were elucidated with multiple techniques including UV–Vis and infrared (IR), electron paramagnetic resonance (EPR), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The results indicate that the monomer has an octahedral symmetry with six water molecules at its six apices. In the dimer, two Cr(III) ions, each of which has an octahedral coordination symmetry distorted by the stretching along the CrCr joining axis, are doubly bridged by two hydroxyl groups. Suggested by the data from EXAFS and EPR, the trimer in solution may form with an irregular triangular configuration, in which two Cr(III) ions are doubly bridged by hydroxyl groups and the third Cr(III) ion is connected to each of the two through single-hydroxyl bridging.Three fundamental chromium(III) hydrolytic oligomers (monomer, dimer, and trimer) were isolated from weakly acidic solutions and their structures were elucidated with multiple techniques including UV–Vis and infrared (IR), electron paramagnetic resonance (EPR), and extended X-ray absorption fine structure (EXAFS) spectroscopy.

Electrospray ionization-mass spectrometry (ESI-MS) shows great promise as a rapid method to identify metal–ligand complexes in solution. However, its application for quantitative determination of the distribution of species present in complicated equilibria is still in its infancy, and a direct correlation between ions observed in the gas phase and species expected in solution must be made with caution. The present work focuses on a seemingly simple system; the complexation of lanthanide cations with the acetate ligand. Using a high resolution quadrupole time-of-flight mass spectrometer, ions created by electrospray of solutions containing trivalent neodymium and acetate were identified. The gas phase distribution of species was compared to the solution phase speciation predicted using thermodynamic complexation constants. Apparent gas phase speciation diagrams were constructed as a function of solution conditions and fragmentation potential. Despite the expected variability of metal–ligand complexes as solution conditions change, the observed gas phase speciation was independent of the metal to ligand ratio but dependent on the operating conditions of the ESI-MS.

Plutonium (Pu), americium (Am), and curium (Cm) activities were measured in sediments from a former radioactive waste disposal basin located on the Savannah River Site, South Carolina, and in subsurface aquifer sediments collected downgradient from the basin. In situ Kd values (Pu concentration ratio of sediment/groundwater) derived from this field data and previously reported groundwater concentration data compared well to laboratory Kd values reported in the literature. Pu isotopic signatures confirmed multiple sources of Pu contamination. The ratio of 240Pu/239Pu was appreciably lower for sediment samples compared to the associated groundwater. This isotopic ratio difference may be explained by the following: (1) 240Pu produced by decay of 244Cm may exist predominantly in high oxidation states (PuVO2+ and PuVIO22+) compared to Pu derived from the disposed waste effluents, and (2) oxidized forms of Pu sorb less to sediments than reduced forms of Pu. Isotope-specific Kd values calculated from measured Pu activities in the sediments and groundwater indicated that 240Pu, which is derived primarily from the decay of 244Cm, had a value of 10 ± 2 mL g–1, whereas 239Pu originating from the waste effluents discharged at the site had a value of 101 ± 8 mL g–1. One possible explanation for the isotope-specific sorption behavior is that 240Pu likely existed in the weaker sorbing oxidation states, +5 or +6, than 239Pu, which likely existed in the +3 or +4 oxidation states. Consequently, remediation strategies for radioactively contaminated systems must consider not only the discharged contaminants but also their decay products. In this case, mitigation of Cm as well as Pu will be required to completely address Pu migration from the source term.

A method for quantifying ratios of isotopes of plutonium (Pu), americium (Am), and curium (Cm) using inductively coupled plasma mass spectrometry (ICP-MS) is described that does not require radiochemical separations or a chemical yield monitor. This approach provides more rapid analysis, which is important for chronometric applications related to nuclear forensics analysis. To demonstrate its utility, we used it to quantify the ingrowth 240Pu (t1/2 = 6563 years) from 244Cm (t1/2 = 18.10 years) in a solution of unknown “age” (e.g. time since last separation). Results are compared to similar samples for which the time since separation was known. In addition, alpha spectrometry was used to validate the ICP-MS measurements. In this case, 238Pu and 241Am were used as chemical yield monitors for 240Pu and 244Cm, respectively. The relative standard deviation for the isotope ratio method using ICP-MS was slightly greater than the traditional radiometric approach, but sufficient for this application. Measured activity ratios of 240Pu and 244Cm provided an age for the unknown sample that linked it to research activities involving the production of curium isotopes for thermoelectric heat sources during the late 1970's.

An evaluation using paraffin oil based, Acheson 38 carbon paste electrodes modified with α-hydroxyisobutyric acid (HIBA) to preconcentrate f-elements cathodically is described. The modified paste was made by directly mixing solid HIBA into the carbon paste. A chemically reversible cyclic voltammogram for HIBA was observed on this modified carbon paste, which was found to be a non-Nerstian, single electron transfer process. Lanthanides (less promethium) were found to accumulate onto the electrode surface during a 30 s electrodeposition step at −0.4 V vs Ag/AgCl from 0.1 M LiCl. The elements were then stripped off into a 2% HNO3 solution by an oxidative step at +0.8 V vs Ag/AgCl; quantitative removal from the electrode was confirmed by ICPMS. Ultratrace solutions with initial concentrations down to 5 parts per quadrillion (ppq) were preconcentrated in 5 min above our instrumental limit of detection (LOD) of around 1 ppt for lanthanides.

Field detection and quantification of f-elements is an important problem in radioanalytical chemistry requiring small, portable devices. Here, characterization of a 10 μm Hg film carbon fiber disk microelectrode to accumulate f-elements is described. Accumulation was performed by cathodic deposition and evaluated by anodic stripping and subsequent ICPMS analyses. La3+ was used as the model element, and subsequent studies were conducted on a 17 element mixture (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Th). In the model studies, La3+ undergoes a sorption phenomenon, and as in other studies and confirmed by ICPMS, a monolayer of atoms on the electrode surface is formed. Dissolved O2 was found to have no effect on the cathodic accumulation of La3+. Consideration of electrode reaction conditions is made, and reactions are hypothesized. The limit of detection (LOD) was found to be 10–7 M with mass detection of 109 atoms, approximately 5 orders of magnitude less than at conventionally sized electrodes. To solve a dilution problem in follow-on analyses, a suggestion to use microelectrode chip-based sensors was made.

An approach to concentrate trivalent lanthanide elements into or onto mercury film electrodes supported on rotating disk glassy carbon electrodes in small volumes (≤1000 μL) is described. La3+ was used as a model for the trivalent f-element cations because its standard potential is the most negative. La3+ cathodically sorbed onto or into a preformed Hg film electrode from LiCl. After initial characterizations, Nd3+, Eu3+, Gd3+, Ho3+, and Lu3+ were tested individually and in a mixture. ICPMS analyses demonstrated that these elements could be accumulated cathodically from LiCl solution and stripped anodically in 2% HNO3, both individually and as a mixture. These cations can be electrochemically preconcentrated onto and stripped from the electrode in 5 min, a vast improvement over traditional approaches such as evaporation that require hours to days in some cases.

Within the pCH range of 2.5 to 4.2, gluconate forms three uranyl complexes UO2(GH4)+, UO2(GH3)(aq), and UO2(GH3)(GH4)−, through the following reactions: (1) UO22+ + GH4− = UO2(GH4)+, (2) UO22+ + GH4− = UO2(GH3)(aq) + H+, and (3) UO22+ + 2GH4− = UO2(GH3)(GH4)− + H+. Complexes were inferred from potentiometric, calorimetric, NMR, and EXAFS studies. Correspondingly, the stability constants and enthalpies were determined to be log β1 = 2.2 ± 0.3 and ΔH1 = 7.5 ± 1.3 kJ mol−1 for reaction (1), log β2 = −(0.38 ± 0.05) and ΔH2 = 15.4 ± 0.3 kJ mol−1 for reaction (2), and log β3 = 1.3 ± 0.2 and ΔH3 = 14.6 ± 0.3 kJ mol−1 for reaction (3), at I = 1.0 M NaClO4 and t = 25 °C. The UO2(GH4)+ complex forms through the bidentate carboxylate binding to U(VI). In the UO2(GH3)(aq) complex, hydroxyl-deprotonated gluconate (GH32−) coordinates to U(VI) through the five-membered ring chelation. For the UO2(GH3)(GH4)− complex, multiple coordination modes are suggested. These results are discussed in the context of trivalent and pentavalent actinide complexation by gluconate.

In acidic aqueous solutions, the protonation of gluconate is coupled with the lactonization of gluconic acid. With a decrease of pCH, two lactones (δ- and γ-) are sequentially formed. The δ-lactone forms more readily than the γ-lactone. In 0.1 mol⋅L−1 gluconate solutions, if pCH>2.5 then only the δ-lactone is generated. When the pCH is decreased below 2.0, formation of the γ-lactone is observed although the δ-lactone still predominates. In solutions with I=0.1 mol⋅L−1 NaClO4 and room temperature, the deprotonation constant of the carboxylic group was determined to be log 10Ka=3.30±0.02 using the NMR technique, and the δ-lactonization constant obtained by batch potentiometric titrations was log 10KL=−(0.54±0.04). Using ESI-MS, the rate constants for the δ-lactonization and the reverse hydrolysis reaction at pCH≈5.0 were estimated to be k1=3.2×10−5 s−1 and k−1=1.1×10−4 s−1, respectively.

A method for quantifying ratios of isotopes of plutonium (Pu), americium (Am), and curium (Cm) using inductively coupled plasma mass spectrometry (ICP-MS) is described that does not require radiochemical separations or a chemical yield monitor. This approach provides more rapid analysis, which is important for chronometric applications related to nuclear forensics analysis. To demonstrate its utility, we used it to quantify the ingrowth 240Pu (t1/2 = 6563 years) from 244Cm (t1/2 = 18.10 years) in a solution of unknown “age” (e.g. time since last separation). Results are compared to similar samples for which the time since separation was known. In addition, alpha spectrometry was used to validate the ICP-MS measurements. In this case, 238Pu and 241Am were used as chemical yield monitors for 240Pu and 244Cm, respectively. The relative standard deviation for the isotope ratio method using ICP-MS was slightly greater than the traditional radiometric approach, but sufficient for this application. Measured activity ratios of 240Pu and 244Cm provided an age for the unknown sample that linked it to research activities involving the production of curium isotopes for thermoelectric heat sources during the late 1970's.