Centrifugal analysis

Most CZE separations are very sensitive to conductivity (e.g., salt concentration) in the run buffer. Therefore, to avoid introducing a high amount of salt from the sample injection, samples should be buffer exchanged with an appropriate low salt buffer prior to analysis. Centrifugal UF/DF devices are ideal for this purpose, as they are typically very reproducible and allow the analyst greater flexibility in controlling the final sample concentration. 

Alkali Metals, In an attempt to establish the existence of the intercalated compound C4K, Herold et al. carried out a detailed experimental analysis of the reaction of molten potassium with graphite. Neither enthalpy analysis, centrifugal separation, dilatometry, nor Jf-ray crystallography gave any evidence for the formation of C4K. 

Before HPLC analysis, centrifuge stored samples (40 pL) for 4 ram (12,000g) and transfer 30 pL of the supernatant to new vials for analysis. Our samples were analyzed using a method of precolumn derivatization with o-pthalaldehyde followed by reversed-phase HPLC and fluonmetric detection (II). 

BS ISO 13318 (2000) Particle size analysis - centrifugal sedimentation methods. British Standards Institution, London. 

In analytical ultracentrifuges, molecular properties can be modeled through sedimentation velocity analysis or sedimentation equilibrium analysis. In sedimentation velocity analysis, concentrations and solute properties are modeled continuously overtime. Sedimentation velocity analysis can be used to determine the macromolecule s shape, mass, composition, and conformational properties. During sedimentation equilibrium analysis, centrifugation has stopped and particle movement is based on diffusion. This allows for modeling of the mass of the particle as well as the chemical equilibrium properties of interacting solutes. 

The general analysis, while not difficult, is complicated however, the limiting case of the very elongated, essentially cylindrical drop is not hard to treat. Consider a section of the elongated cylinder of volume V (Fig. II-18h). The centrifugal force on a volume element is u rAp, where w is the speed of revolution and Ap the difference in density. The potential energy at distance r from the axis of revolution is then w r Apfl, and the total potential energy for the... 

Flow injection analysis (FIA) was developed in the mid-1970s as a highly efficient technique for the automated analyses of samples. °> Unlike the centrifugal analyzer described earlier in this chapter, in which samples are simultaneously analyzed in batches of limited size, FIA allows for the rapid, sequential analysis of an unlimited number of samples. FIA is one member of a class of techniques called continuous-flow analyzers, in which samples are introduced sequentially at regular intervals into a liquid carrier stream that transports the samples to the detector. ... 

The reaction mixture can either be crystallised, centrifuged, and dried, or spray-dried and cyclone-separated to produce a fine crystalline powder having a particle size of 50 p.m. Metal analysis of the AP produced by this method is reported to be less than 0.02 p.g/g. 

Sedimentation (qv) techniques, whether based on gravitational forces or centrifugation, derive the particle size from the measured travel rates of particles in a Hquid. Before the particle analysis is carried out, the sample is usually dispersed in a medium to break down granules, agglomerates, and aggregates. The dispersion process might involve a simple stirring of the powder into a Hquid, but the use of an ultrasonic dispersion is preferred. 

Sediment Volume. If the dispersion is unstable, the sediment bed will be quite deep and sedimenting particles will stick together where they first strike the sediment bed, thus forming an open stmcture with considerable occluded Hquid. If the dispersion is stable to reagglomeration, the particles will move freely past one another to avoid contact as long as possible. The result is a thin sediment bed with maximum soHds packing and minimum occluded hquid (12). Since dispersed particles setde more slowly than docs, centrifugation maybe needed to force sedimentation of small particles within a reasonable analysis time. 

Biomolecule Separations. Advances in chemical separation techniques such as capillary zone electrophoresis (cze) and sedimentation field flow fractionation (sfff) allow for the isolation of nanogram quantities of amino acids and proteins, as weU as the characterization of large biomolecules (63—68) (see Biopolymers, analytical techniques). The two aforementioned techniques, as weU as chromatography and centrifugation, ate all based upon the differential migration of materials. Trends in the area of separations are toward the manipulation of smaller sample volumes, more rapid purification and analysis of materials, higher resolution of complex mixtures, milder conditions, and higher recovery (69). 

The Bottle Centrifuge. Analysis of the performance of a botde centrifuge is based on the model shown in Figure 1. A soHd or Hquid particle is considered in an initial position, X, at a radius, r, from the axis of rotation. If equation 2 is appHed to this specific particle, assuming that = dr/dt then... 

The Z-concept permits scale-up between sinulat centrifuges solely on the basis of sedimentation performance. Other criteria and limitations, however, should also be investigated. Scale-up analysis for a specified sohds concentration, for instance, requires knowledge of sohds residence time, permissible accumulation of sohds in the bowl, G level, sohds conveyabihty, flowabihty, compressibihty, limitations of torque, and sohds loading. Extrapolation of data from one size centrifuge to another calls for the apphcation of specific scale-up mechanisms for the particular type of centrifuge and performance requirement. 

Fig. 4. Aggregate size distributions by electron microscope image analysis (D and centrifugal (Z9 sedimentations for N220 and N351 carbon blacks (8).

For determination of the aerodynamic diameters of particles, the most commonly apphcable methods for particle-size analysis are those based on inertia aerosol centrifuges, cyclones, and inertial impactors (Lundgren et al.. Aerosol Measurement, University of Florida, Gainesville, 1979 and Liu, Fine Paiiicles—Aerosol Generation, Measurement, Sampling, and Analysis, Academic, New York, 1976). Impactors are the most commonly used. Nevertheless, impactor measurements are subject to numerous errors [Rao and Whitby, Am. Ind. Hyg. A.s.soc.]., 38, 174 (1977) Marple and WiUeke, "Inertial Impactors, in Lundgren et al.. Aerosol Measurement and Fuchs, "Aerosol Impactors, in Shaw, Fundamentals of Aerosol Sci-... 

Imperforate Bowl Tests The amount of supernant hquid from spin tubes is usually too small to warrant accurate gravimetric analysis. A fixed amount of shiny is introduced at a controlled rate into a rotating imperforate bowl to simulate a continuous sedimentation centrifuge. The liquid is collected as it overflows the ring weir. The test is stopped when the solids in the bowl build up to a thickness which affects centrate quality. The solid concentration of the centrate is determined similarly to that of the spin tube. 

The useful parameter for value analysis is the installed cost of the number of centrifuges required to produce the demanded separative effecd (end product) at the specified capacity of the plant. The possible benefits of adjustments in the upstream and downstream components of the plant and the process should be carefully examinee in... 

While the foregoing examples have dealt with applications on centrifugal pumps, the same sort of analysis can be made for reciprocating pumps, reciprocating compressors, or other rotary users hke cooling-tower fans. 

So in this chapter of failure analysis and corrective methods, we decided to consider some problems, symptoms, and remedies particular to PD pumps. We re using two tables. The first table lists the few symptoms that send a PD pump into the shop. These symptoms are mated to another column of possible causes listed in numerical order. The numerical causes are on the second tabic starting with the. source of the problem in the left column and the probable cause/suggested remedy in the right column. As you go through the list, you ll see again that PD pumps and centrifugal pumps have a lot in common. Enjoy. 

Dawes, W., 1995, A Simulation of the Unsteady Interaction of a Centrifugal Impeller with its Vaned Diffuser Flows Analysis, ASME Journal of Turbomachinery, Vol. 117, pp. 213-222. 

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