Sedimentation separation power

In the analytical scheme, besides the sampling and the final analysis, the sample preparation and cleanup are also crucial. Sample preparation plays an important role in the analysis of FRs in environmental samples because of the complex matrices and only trace levels of analytes. Solid and semisolid samples are usually first dried and homogenized. Then the FRs are extracted from the sample (solid or liquid), and the extract is usually purified, fractionated, and concentrated before the final analysis, which is typically performed with gas or liquid chromatography. The extraction procedure is dependent on the sample matrix different methods are used for sediment, tissue, and liquid samples. After extraction, it will usually be necessary to purify and fractionate the extract, because most extraction methods are insufficiently selective and the separation power of the analytical technique not sufficient. Extracts typically contain several analytes similar to the FRs, which may be present in much higher quantities. The fractionation procedures are similar for the different types of extracts. Typical analytical procedures are given in Tables 31.2 to 31.6. 

The hydrocyclone, commonly referred to simply as cyclone, is a nonmechanical sedimentation-type classifier (2,6,10,27) (Fig. 7). It has no moving parts or power attachments directly connected to it. The hydrocyclone has become the workhorse of most mineral processing operations because of its simplicity, short residence time, compactness, and low cost of operation. It is, however, characterized by lack of sharpness of separation. Equipment... 

Surface spectroscopic techniques must be separated carefully into those which require dehydration for sample presentation and those which do not. Among the former are electron microscopy and microprobe analysis, X-ray photoelectron spectroscopy, and infrared spectroscopy. These methods have been applied fruitfully to show the existence of either inner-sphere surface complexes or surface precipitates on minerals found in soils and sediments (13b,30,31-37), but the applicability of the results to natural systems is not without some ambiguity because of the dessication pretreatment involved. If independent experimental evidence for inner-sphere complexation or surface precipitation exists, these methods provide a powerful means of corroboration. 

In a solution, particles whose density is higher than that of the solvent sink (sediment), and particles that are lighter than it float to the top. The greater the difference in density, the faster they move. If there is no difference in density (isopyknic conditions), the particles hover. To take advantage of even tiny differences in density to separate various particles in a solution, gravity can be replaced with the much more powerful centrifugal force provided by a centrifuge. 

Sedimentation in an ultracentrifuge is a powerful means for separating biological particles and large macromolecules. Sedimentation is the only static field (Sc) method other than electrophoresis (in all of its various forms) commonly used for multicomponent separations. 

The basic experimental equipment for FFF is, except for the channel and its support, in general identical to the equipment used for liquid chromatography. It is usually composed of a solvent reservoir, a pump, and an injection system the chromatographic column is replaced by the FFF channel, followed by a detector. The FFF channel can require additional supporting devices, such as a centrifuge for sedimentation FFF or a power supply, and other electronic regulation devices for electrical FFF. If necessary, this basic equipment is complemented by a flow meter at the end of the separation system. For special semipreparative purposes, a fraction collector can be attached to the system. 

A full account of the problems considered in collecting, storing, and processing marine samples for transuranic analysis is given in the above-mentioned review (4). The specific methods discussed here were foimd effective at least for the transuranic analyses of seawater and sediments contaminated by global fallout, nuclear fuel reprocessing wastes, or nuclear power plant operation waste. In these cases, a preliminary acid treatment of the sample in the presence of suitable yield monitors seems to solubilize the transuranic elements and achieves isotopic equilibration between the yield monitor and sample. The yield monitors used were either Pu or sep qj. 238,239,240,24ip whereas Am was used for Am, 2 Cm, and by inference, Cf. In addition, it was convenient to use 50 mg of a lanthanide (neodymium) as a carrier for americium to purify the separated americium fraction. 

Figure I. Illustration of the high resolving power of FFF for the separation of particles in different size ranges a, submicrometer polystyrene latex microspheres fractionated by power-programmed normal mode sedimentation FFF and b, supramicrometer-sized latex spheres fractionated by sedimenta-...

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