Shane M. Peper

Plasticizer-Free Polymer Membrane Ion-Selective Electrodes Containing a Methacrylic Copolymer Matrix

A methyl methacrylate and decyl methacrylate (MMA-DMA) copolymer has been used to fabricate plasticizer-free ion-selective membranes. The copolymer matrix showed good mechanical properties, and can be solvent cast in complete analogy to traditional ISE membranes. The material was evaluated in ionophore-free cation and anion exchanger membranes as well as in ion-selective electrode membranes containing five different neutral ionophores. The selectivity of Na (X) based copolymer membranes was found to be superior when compared to corresponding membranes made from poly(vinyl chloride) plasticized with bis(2-ethylhexyl sebacate) (PVC-DOS) and other plasticizer free membranes. Other ionophore-based MMA-DMA membranes, with the exception of magnesium-selective systems, also showed excellent selectivity similar to the corresponding PVC-DOS membranes. This makes MMA-DMA a potentially superior choice over alternative membrane matrices reported in the literature and a promising platform for the establishment of covalently immobilized membrane components.

Cross-linked dodecyl acrylate microspheres: novel matrices for plasticizer-free optical ion sensing

Hexanedioldiacrylate (HDDA) cross-linked dodecyl acrylate (DDA) microspheres ranging from approximately 1 to 10m in diameter have been prepared via photoinitiated dispersion polymerization and used as polymer matrices in the development of a new class of “plasticizer-free” ion-selective optical sensors (optodes). Incorporation of a fluorescent Nile Blue derivative (ETH 5294) into the microspheres produced independent self-referencing optodes capable of measuring the activities of various anions in aqueous media. In order to increase sensitivity and signal reproducibility, changes in the fluorescence intensity of two emission peaks, corresponding to the protonated and deprotonated forms of the chromoionophore, were used to perform ratiometric analysis. Spatial and 3D spectral resolution of individual sensing microspheres is reported, providing analytically useful information about the local sensing environment. Physical properties of the polymeric microspheres that affect sensor function such as size, morphology, surface topography, dispersity, and glass transition temperature (Tg) are also reported here.

Cs+-selective membrane electrodes based on ethylene glycol-functionalized polymeric microspheres

A new strategy for improving the robustness of membrane-based ion-selective electrodes (ISEs) is introduced based on the incorporation of microsphere-immobilized ionophores into plasticized polymer membranes. As a model system, a Cs(+)-selective electrode was developed by doping ethylene glycol-functionalized cross-linked polystyrene microspheres (P-EG) into a plasticized poly(vinyl chloride) (PVC) matrix containing sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate (TFPB) as the ion exchanger. Electrodes were evaluated with respect to Cs(+) in terms of sensitivity, selectivity, and dynamic response. ISEs containing P-EG and TFPB that were plasticized with 2-nitrophenyl octyl ether (NPOE) yielded a linear range from 10(-1) to 10(-5)M Cs(+), a slope of 55.4 mV/decade, and a lower detection limit (log a(Cs)) of -5.3. In addition, these membranes also demonstrated superior selectivity over Li(+), Na(+), and alkaline earth metal ion interferents when compared to analogous membranes plasticized with bis(2-ethylhexyl) sebacate (DOS) or membranes containing a lipophilic, mobile ethylene glycol derivative (ethylene glycol monooctadecyl ether (U-EG)) as ionophore.

Synthesis, crystallographic characterization, and conformational prediction of a structurally unique molecular mixed-ligand U(VI) solid, Na6[UO2(O2)2(OH)2](OH)2·14H2O

Abstract The first mononuclear molecular mixed-ligand U(VI) solid containing hydroxide and peroxide ligands, Na6[UO2(O2)2(OH)2](OH)2·14H2O (I), was synthesized and structurally characterized using single crystal X-ray diffraction. The crystal structure of I consisted of [UO2(O2)2(OH)2]4− molecular units, with a uranyl(VI) moiety perpendicular to 6 equatorial O atoms belonging to two side-on trans peroxo groups and two terminal trans hydroxo groups. Density functional theory (DFT) calculations determined that the trans -conformer of the [UO2(O2)2(OH)2]4− molecular unit found in I was 24 kcal/mol lower in energy than the previously proposed cis -conformer. Crystal data: monoclinic, space group P21/n with a=13.357(4) Å, b=5.8521(15) Å, c=15.948(6) Å, β=112.292(4)°, and Z=2.

Accelerated analyte uptake on single beads in microliter-scale batch separations using acoustic streaming: plutonium uptake by anion exchange for analysis by mass spectrometry.

The use of acoustic streaming as a noncontact mixing platform to accelerate mass-transport-limited diffusion processes in small-volume heterogeneous reactions has been investigated. Single-bead anion exchange of plutonium at nanomolar and subpicomolar concentrations in 20 microL liquid volumes was used to demonstrate the effect of acoustic mixing. Pu uptake rates on individual approximately 760 microm diameter AG 1 x 4 anion-exchange resin beads were determined using acoustic mixing and compared with Pu uptake rates achieved by static diffusion alone. An 82 MHz surface acoustic wave (SAW) device was placed in contact with the underside of a 384-well microplate containing flat-bottomed semiconical wells. Acoustic energy was coupled into the solution in the well, inducing acoustic streaming. Pu uptake rates were determined by the plutonium remaining in solution after specific elapsed time intervals using liquid scintillation counting (LSC) for nanomolar concentrations and thermal ionization mass spectrometry (TIMS) analysis for the subpicomolar concentration experiments. It was found that this small batch uptake reaction could be accelerated by a factor of about 5-fold or more, depending on the acoustic power applied.

Structure and Bonding Investigation of Plutonium Peroxocarbonate Complexes Using Cerium Surrogates and Electronic Structure Modeling

Herein, we report the synthesis and structural characterization of K8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O. This is the second Pu-containing addition to the previously studied alkali-metal peroxocarbonate series M8[(CO3)3A]2(μ-η2-η2-O2)2·xH2O (M = alkali metal; A = Ce or Pu; x = 8, 10, 12, or 18), for which only the M = Na analogue has been previously reported when A = Pu. The previously reported crystal structure for Na8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O is not isomorphous with its known Ce analogue. However, a new synthetic route to these M8[(CO3)3A]2(μ-η2-η2-O2)2·12H2O complexes, described below, has produced crystals of Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O that are isomorphous with the previously reported Pu analogue. Via this synthetic method, the M = Na, K, Rb, and Cs salts of M8[(CO3)3Ce]2(μ-η2-η2-O2)2·xH2O have also been synthesized for a systematic structural comparison with each other and the available Pu analogues using single-crystal X-ray diffraction, Raman spectroscopy, and density functional theory calculations. The Ce salts, in particular, demonstrate subtle differences in the peroxide bond lengths, which correlate with Raman shifts for the peroxide Op-Op stretch (Op = O atoms of the peroxide bridges) with each of the cations studied: Na+ [1.492(3) Å/847 cm-1], Rb+ [1.471(1) Å/854 cm-1], Cs+ [1.474(1) Å/859 cm-1], and K+ [1.468(6) Å/870 cm-1]. The trends observed in the Op-Op bond distances appear to relate to supermolecular interactions between the neighboring cations.

FY-2010 Process Monitoring Technology Final Report

During FY 2010, work under the Spectroscopy-Based Process Monitoring task included ordering and receiving four fluid flow meters and four flow visible-near infrared spectrometer cells to be instrumented within the centrifugal contactor system at Pacific Northwest National Laboratory (PNNL). Initial demonstrations of real-time spectroscopic measurements on cold-stream simulants were conducted using plutonium (Pu)/uranium (U) (PUREX) solvent extraction process conditions. The specific test case examined the extraction of neodymium nitrate (Nd(NO3)3) from an aqueous nitric acid (HNO3) feed into a tri-n-butyl phosphate (TBP)/ n-dodecane solvent. Demonstration testing of this system included diverting a sample from the aqueous feed meanwhile monitoring the process in every phase using the on-line spectroscopic process monitoring system. The purpose of this demonstration was to test whether spectroscopic monitoring is capable of determining the mass balance of metal nitrate species involved in a cross-current solvent extraction scheme while also diverting a sample from the system. The diversion scenario involved diverting a portion of the feed from a counter-current extraction system while a continuous extraction experiment was underway. A successful test would demonstrate the ability of the process monitoring system to detect and quantify the diversion of material from the system during a real-time continuous solvent extraction experiment. The system was designed to mimic a PUREX-type extraction process with a bank of four centrifugal contactors. The aqueous feed contained Nd(NO3)3 in HNO3, and the organic phase was composed of TBP/n-dodecane. The amount of sample observed to be diverted by on-line spectroscopic process monitoring was measured to be 3 mmol (3 x 10-3 mol) Nd3+. This value was in excellent agreement with the 2.9 mmol Nd3+ value based on the known mass of sample taken (i.e., diverted) directly from the system feed solution.

FY 2009 Progress: Process Monitoring Technology Demonstration at PNNL

Pacific Northwest National Laboratory (PNNL) is developing and demonstrating three technologies designed to assist in the monitoring of reprocessing facilities in near-real time. These technologies include 1) a multi-isotope process monitor (MIP), 2) a spectroscopy-based monitor that uses UV-Vis-NIR (ultraviolet-visible-near infrared) and Raman spectrometers, and 3) an electrochemically modulated separations approach (EMS). The MIP monitor uses gamma spectroscopy and pattern recognition software to identify off-normal conditions in process streams. The UV-Vis-NIR and Raman spectroscopic monitoring continuously measures chemical compositions of the process streams including actinide metal ions (uranium, plutonium, neptunium), selected fission products, and major cold flow sheet chemicals. The EMS approach provides an on-line means for separating and concentrating elements of interest out of complex matrices prior to detection via nondestructive assay by gamma spectroscopy or destructive analysis with mass spectrometry. A general overview of the technologies and ongoing demonstration results are described in this report.

Procedure 2 Determination of cesium in natural waters using polymer-based ion-selective electrodes

Publisher Summary This chapter discusses a cesium-selective electrode based on the recommendations for obtaining unbiased selectivity coefficients and optimal detection limit. Sensor preparation and sample treatment are described, includingmembrane preparation, inner solution preparation, and electrode preparation. The determination of cesium was attempted in three different natural water samples—tap water from a laboratory at DCU, a sample from the Tolka river, which runs through the city of Dublin, Ireland and a rainwater sample. For the determination of selectivity coefficients, the calibration curves of each interfering ion and Cs + were recorded separately using electrodes prepared. Selectivity coefficients were obtained by the modified separate solution method, which allows for the determination of unbiased selectivity coefficients. The optimization of the low detection limit (LDL) is done according to current understanding of the underlying mechanisms that dictate the potential response of ion -selective electrodes. Reducing the zero-current ion fluxes within the membrane, which is a major factor that introduces biases in the LDL measurements, was performed by optimisation of the membrane parameters and inner solution.