Solvent-impregnated resins columns

The development of solvent-impregnated resins and extraction-chromatographic procedures has enabled the automation of radiochemical separations for analytical radionuclide determinations. These separations provide preconcentration from simple matrices like groundwater and separation from complex matrixes such as dissolved sediments, dissolved spent fuel, or nuclear-waste materials. Most of the published work has been carried out using fluidic systems to couple column-based separations to on-line detection, but robotic methods also appear to be very promising. Many approaches to fluidic automation have been used, from individual FI and SI systems to commercial FI sample-introduction systems for atomic spectroscopies. 

An impregnated resin prepared from PC-88A and Amberlite XAD7 beads was examined as the stationary column phase for the separation of rare earth [28]. The reagent, PC-88A, is frequently used as an extractant in rare earth separation by solvent extraction. As can be seen in Fig. 27, the distribution ratio at a given pH increases with decreasing ionic radii of lanthanides. The slope analysis for log D versus pH and log D versus concentration of PC-88A indicated that the present extraction mechanism was similar to that of the solvent extraction system. A mutual separation of Y-Gd, La-Pr-Nd, and Ho-Er-Tm was successfully attained with the present resin as the stationary phase and hydrochloric acid as the mobile phase. 

Major matrix components or other trace organic compoimds, such as polycyclic aromatic hydrocarbons (PAH) and pesticides, are coextracted with PCBs and might cause interference to the instrumental response, thus they should be eliminated by suitable cleanup procedures. The cleanup is generally performed by column chromatography on suitably activated or deactivate silica [24,54,68,97,128,138,146], sulfuric acid impregned silica [131], alumina [9,14,15,90-92,142], or Florisil (synthetic magnesium silicate) [24,44,67,83], and styrene-divinylbenzene resin [121]. Multilayer columns are frequently utilized. The retention of analytes in the column should be checked by standard solutions in order to find both the best solvent or mixture of solvents and the optimum volume to be used to selectively elute PCBs and leave interferents in the column. n-Hexane and dichloromethane are the most widely used solvents to elute the PCBs from the stationary phase. In addition, special treatments are very often used to eliminate specific interfering substances. For instance, activated copper powder with [23] or without mercury [14,49,81,87,151] or tetrabutyl ammonium sulfite [4] is used to remove elemental sulfur and sulfuric acid is used to remove lipids [107]. 

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