Sedimentation procedure

Turbidimetric methods for particle size analysis (Refs 10, 16 27) are used in conjunction with sedimentation procedures to determine the concn of particles at given distances below the surface at successive time intervals. From these data, and Stokes law, particle size distribution can be calculated... 

The usual problems encountered with any sedimentation procedure are present. It is necessary to use a dispersing liq compatible with the material being tested. Also, dispersing agents and technique must insure complete dispersion and prevent agglomeration. These factors may vary with materials, and therefore will require special attention when new materials are to be analyzed... 

MIP are often generated as simple bulk polymers to be ground into fine particles, which are subsequently sieved and sedimented - admittedly a time-consuming process, which requires large amounts of solvents. The loss of fine polymer particles in the sedimentation procedure is also not negligible. The result usually is a polymer powder with particle sizes of a relative broad size distribution. After the template has been extracted, this material can be packed into LC-columns [17,29,30], CE-capillaries, or be used directly in the batch mode. 

Adsorption column preparation and loading. In order to obtain satisfactory results, the tube must be uniformly packed with the adsorbent uneven distribution may lead to the formation of cracks and channels and to considerable distortion of adsorption band shapes. If there is any doubt concerning the uniformity of particle size of the adsorbent powder it should be sifted before use to remove the larger particles fines are removed from the adsorbent using a sedimentation procedure immediately prior to column packing. In this the alumina or silica gel adsorbent is stirred into between five to ten times its volume of the selected solvent or solvent system, allowed to settle for five minutes and the supernatant liquor decanted off the procedure is repeated until the supernatant liquid is clear. 

Montgomery, E. M., and Senti, F. R. (1958). Separation of amylose from amylopectin of starch by an extraction-sedimentation procedure./. Polym. Sci. 28 1-9. 

A comparison of the procedure outlined for determining particle-size indicates that the diameters so obtained correspond with the de diameters of sedimentation procedures. Fairs attributes this correspondence to areal matching inherent in his technique. However, agreement with surface diameters determined by turbidimeter was not wholly satisfactory. 

It is not always easy to determine what procedure to follow in making a particle-size distribution. Obviously, if the particles are soluble in water or any other fluid, sedimentation procedures must be applied with caution. It is likewise clear that any sedimentation technique is markedly affected by the shape of the particles used, and that results are subject to interpretation. In other words, determinations depending upon sedimentation (and elutriation) are merely equivalent measures of spheres having the same rate of settling. Greatest reliance naturally applies to that size range whose motion is known to be specified by Stokes law. 

Sedimentation procedures to evaluate particle size in terms of the equivalent spheres, which have the same... 

The spleen was removed and cut into several small pieces and was gently forced through a 400 mesh stainless steel screen into a Petri dish which also contained RPMI medium. The cell suspension was transferred to a sterile centrifuge tube and any large tissue aggregates were removed by the sedimentation procedure described by Shortman et al. (lfi). The suspension was centrifuged (200 x g) for 10 minutes and the cell pellet was resuspended in fresh medium. 

Removal of the fines is accomplished with the following sedimentation procedure. Suspend the sieved particles in approximately 100 mL acetone in a 200 mL Erlenmeyer flask. Shake the flask briefly, and then allow the mixture to sit undisturbed. After 30 min, decant the acetone (which contains suspended fines), taking care not to disturb the particles that had settled to the bottom of the flask. Repeat this procedure as many times as necessary until the supernatant is clear (this usually requires 3-5 cycles). Figure 10a shows an SEM image of the particles obtained by this procedure. The size of these particles, which ranges from 10 to 25 pm in diameter, is appropriate for chromatography applications. For a comparison, spherical beads are presented in Fig. 10b these can be easily prepared by various methods, which are discussed in more detail in Chapter 17. 

Fig. 2a,b. Estimation of DNA strand breaks by the nucleoid sedimentation procedure, a Sedimentation of nucleoids from HL-60 cells either exposed to 7-radiation b treated with the indicated concentration of DMS for 15 min... 

Aluminium production whereby sodium hydroxide leaches sodium aluminate in bauxite, from insoluble gibbsite. A sedimentation procedure, usually in the form of a counter-current thickener wash train (see Figure 6.17) is followed by polishing filtration prior to precipitation of alumina trihydrate which is filtered prior to smelting. The flocculants used are typically 100% anionic homopolymers at the front end of the wash... 

The first line start sedimentation procedure based on centrifugal sedimentation was described by Marshall [46], who was aware of the problems involved in floating a layer of suspension onto a column of clear fluid because of reported difficulties with the Werner sedimentation tube discussed in the previous section. He attempted to achieve a stable suspension system by using a suspension of lower density than the liquid column through which the fineparticles were to be sedimented. He used a sucrose solution for the column fluid and a water-based suspension of fineparticles. This strategy as discussed earlier only eliminates gross inversion of the layer of suspension. 

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