Target elution

After several elution and drying cycles, it was possible to maintain target elution at a few tenths of a percent in unirradiated control tests but not in actual irradiation tests. Some temperature increase occurs during irradiation, and, as shown in Table III, temperatures above 100° C cause a marked increase in target elution. 

One might expect some of the metal to be exchangeable after heat treatment, possibly in pores at the crystal surface or in other accessible sites. After such loosely held material is eluted, however, one would expect the remaining metal to remain fixed. The fact that treatment such as evaporation at room temperature can cause an increase in target elution indicates that, even under very mild conditions, a small fraction of the metal atoms may exchange or migrate from inaccessible sites to sites accessible to elution. 

This aspect of the problem is critical because it is the elution of target material which dilutes the product and ultimately limits the isotopic enrichment that can be obtained. Under the rather poorly controlled conditions of reactor irradiations, target elution was generally near 1%. A substantial decrease in target elution would really make this process attractive, and indeed this is the primary factor that can provide a significant improvement in the process. 

Actinides, unlike lanthanides, are a emitters. Tests made with 243Am, 241Am, and 244Cm, which have a radiation intensities (or a decay constants) in the ratio 1 17 435, gave very similar results in regard to both target elution and product yield. Therefore, if a radiation is responsible for the difference, the effect is independent of a intensity. 

At this time it is not clear whether or not the isotopic enrichment described here can be accomplished at a neutron exposure high enough to yield a really useful product, but indications are that a highly thermalized neutron source may yield such products. An alternative development, which would yield a higher enrichment factor or comparable enrichment at lower neutron exposures, would be some means to decrease target elution to much less than 1%. 

The SPE cartridge is then washed with approximately 20mL of 40% methanol in water and then the PFFAs of interest are eluted with approximately 30mL of 100% methanol and the eluate collected. The target elution is then evaporated under nitrogen gas to 0.5mL. 

Components of a mixture emerging from a liquid chromatographic column are dissolved in the eluting solvent, and this solution is the one directed across the target, as described above. Thus, as the components reach the target, they produce ions. These ions are recorded by the spectrometer as an ion current. 

By allowing any solution, but particularly the eluant from a liquid chromatographic column, to flow continuously (dynamically) across a target area under bombardment from fast atoms or ions (FAB or FIB), any eluted components of a mixture are ionized and ejected from the surface. The resulting ions are detected and recorded by a mass spectrometer. The technique is called dynamic FAB or dynamic LSIMS. 

Taking into consideration the fact that initial targets have to be formulated and that the projected targets have to be inspected and adapted, we estimate the pure elution profiles instead of the pure spectra. Therefore, the PCA is carried out in the elution time space and the resulting principal components represent abstract elution profiles (see Fig. 34.6). The factors we are looking for are the elution profiles of the different compounds. The first abstract factor closely resembles one... 

P.J. Gemperline, A priori estimates of the elution profiles of the pure components in overlapped liquid chromatography peaks using target factor analysis. J. Chem. Inf. Comput. Sci., 24 (1984) 206-212. 

Subsequently, elute the target substance with 50 mL of the same buffer solution containing 0.1 M sodium chloride. Transfer this eluate to a 200-mL separatory funnel,... 

This technique is based on the same separation mechanisms as found in liquid chromatography (LC). In LC, the solubility and the functional group interaction of sample, sorbent, and solvent are optimized to effect separation. In SPE, these interactions are optimized to effect retention or elution. Polar stationary phases, such as silica gel, Florisil and alumina, retain compounds with polar functional group (e.g., phenols, humic acids, and amines). A nonpolar organic solvent (e.g. hexane, dichloromethane) is used to remove nonpolar inferences where the target analyte is a polar compound. Conversely, the same nonpolar solvent may be used to elute a nonpolar analyte, leaving polar inferences adsorbed on the column. 

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