Resin-bead technique

The oxalate precipitation and subsequent calcination to the oxide is reserved for multimicrogram and greater quantities of actinides and for Es-253, whose intense radiation precludes the use of the resin bead technique. The preparation of fluoride compounds is not carried out in quartz but in Monel (6) Details of the conditions of temperature, pressure, etc. to effect these chemical reactions are available in the literature Cl>3,6-11) ... 

Malinowski J (1967) Precise determination of uranium in pure metal and uranium compounds by constant current coulometry Talanta 14 283 Marsh SF, Ortiz MR, Abernathey RM, Rein JE (1974) Improved 2-column ion exchange separation of plutonium, uranium and neodymium in mixed U/Pu fuels for burn up measurements, LA5568 Marsh SF, Abernathey RM, Rein JE (1981) Evaluation of treatments to attain isotopic equilibration of plutonium preceding the resin bead technique for mass spectrometric assay analysis of spent reactor fuel. In Minutes 4th SALE participants meeting, Argonne, p 218 Anal Lett 13 1487... 

An approach similar to the resin-bead technique employed activated charcoal chunks in place of the beads. The actinide was sorbed on a chunk of charcoal, and after calcination in air to remove the carbon, a low-density oxide particle could be recovered (Haire 1982). This approach has been used with Es, but in general the procedure yielded less satisfactory particles than the resin technique. 

The solid-phase technique of split and mix synthesis relies on the efficiency of mixture-based synthesis to provide very large libraries (millions) of discrete compounds (Figure 4).[161 In this approach, each resin bead is treated with a single building block for each synthesis step. Thus any single resin bead possesses identical copies of one library member, but the identity of the library member on any bead is lost due to the mix step of the process. Elegant strategies have been developed to chemically encode the syn-... 

As first practiced by Geysen and Houghton, the preparation of combinatorial libraries produced discrete compounds of known identity through a technique known as "spatial separation," which simply means that individual compounds in the library are produced discretely and are not mixtures. Such spatially addressable compound sets are produced in such a way as to keep separate the reaction flasks or resin beads containing the individual components of the library and perform bioassays on the discrete compounds, one at a time. Thus, if the "history" of the reaction conditions performed in each flask or on each solid support, the identity of the compounds produced is known, without resort to structure elucidation techniques. Initially, this technique, after typically an extensive reaction development stage, allowed the preparation of between 10 and 1000 discrete combinatorial products. 

An isotope dilution mass spectrometric method involves the addition of a known quantity of Tc followed by chemical separation, purification, and measurement of the Tc/ Tc isotopic ratio . An improved technique has been developed for the analysis of Tc in environmental samples. After spiking with Tc the isolated technetium is concentrated onto anion exchange beads. Determination of as little as 1 pg has been achieved through the enhanced ionization efficiency afforded by the resin bead source ... 

The Furka method produces the library of compounds on resin beads. It may be used to make both large (thousands) and small (hundreds) combinatorial libraries. Large libraries are possible because the technique produces one type of compound on each bead, that is, all the molecules formed on one bead are the same but different from those formed on all the other beads. Each bead will yield up to 6 x 1013 product molecules, which is sufficient to carry out high throughput screening procedures. The technique has the advantage that it reduces the number of reactions required to produce a large library. 

An example of a 3x3x3 combinatorial split and mix combinatorial synthesis is shown in Figure 15.2. The technique involves three initial batches of resin beads to which are initially coupled, for example, a different amino acid. These batches are then combined, mixed and split again into three batches each batch now containing a mixture of beads containing different amino acids. A different amino acid is then coupled to each of these batches of beads, the beads mixed, split and the process repeated a third time. This simple... 

Resin-bead loading and calcination techniques have been used to produce all curium and americium oxide feed material... 

The use of mass spectrometry (MS) techniques to monitor SP reactions has recently become possible through the use of matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) spectrometry (137) after in situ cleavage of a small number of resin beads (138-140). Although the compound is cleaved from the resin, the cleavage happens directly onto the center of the MALDI target and the method can be considered on-bead. 

The use of infrared (IR) spectroscopy as a reaction monitoring technique for SPS has become more frequent over the last few years with the introduction of technologies specifically aimed toward SP reactions. Even so, a number of reports describing the use of classical IR by thorough mixing of a few milligrams of grounded resin beads in KBr pellets have appeared (150, 151). 

Despite the high cost of the equipment required and the time taken for sample preparation and spectra acquisition, MAS-HR NMR provides invaluable stmctural information about the species present in a reaction. Only a few milligrams of resin beads are required and they can be recovered as the technique is nondestructive. The complementarity of the technique with other analytical methods is clear MALDl-TOP cannot discriminate among compounds with the same MW and depends on the ionization properties of the resin-bound compound, while PTIR depends on the presence of selected functional groups in the molecule. MAS-HR NMR can be used independently from the nature of the performed reaction and the functional groups formed or lost during the SPS step. Additionally, two-dimensional MAS techniques such as 2D-COSY (correlated spectroscopy) and TOCSY (total correlated spectroscopy) (171) or 2D-SECSY (spin echo correlation spectroscopy) (181) can provide more detailed information that may be useful in specific cases. 

Resin beads, which can be considered as individual microreactors, allow the use of mix-and-split techniques, which are not applicable when using homogeneous reaction conditions. 

The switch from single compounds to a combinatorial library in solution increases the complexity of the potential issues to be addressed, as we have seen in the previous chapters. The same is true for the purification of these libraries, which cannot rely on simple filtration and washing of the resin beads, as in the SP chemistries. The separation techniques of classical chemistry are used. However, general, automated methods applicable to all members of a library have to be found. Usually, these methods are also applicable to the final purification of cleaved SP libraries, either as discretes or as pools. 

Carman (C6) described the successful development and application to a uranium resin-in-pulp process of a continuous countercurrent ion-exchange pilot plant. This new technique is based on the observation that the resins at the correct level of air agitation float in close proximity to the surface of the pulp. So long as the resin beads are able to move about gently but freely in the surface layer, a satisfactory rate of ion exchange is possible. Under this condition, the mechanical damage to the resin due to attrition is negligible. 

Mass spectroscopy is the basic technique used for isotopic analysis. It is also used to determine the concentrations for fissile elements in samples that have been diluted and thus contain too little uranium and plutonium for accurate assay by standard wet chemical techniques. A tracer technique, known as isotope dilution analysis, is used in such cases, particularly with irradiated spent fuel or resin bead samples. 

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