Density gradients mixtures

Illustration showing separation by equilibrium-density-gradient centrifugation. The homogeneous mixture in (a) separates into three bands (b) after applying centrifugal force. 

Density gradients to stabilize flow have been employed by Philpot IT> Yin.s. Faraday Soc., 36, 38 (1940)] and Mel [ j. Phys. Chem., 31,559 (1959)]. Mel s Staflo apparatus [J. Phys. Chem., 31, 559 (1959)] has liquid flow in the horizontal direction, with layers of increasing density downward produced by sucrose concentrations increasing to 7.5 percent. The solute mixture to be separated is introduced in one such layer. Operation at low electrolyte concentrations, low voltage gradients, and low flow rates presents no cooling problem. 

In this approach a mixed solvent is chosen so that the relative sedimentation of the two components may give rise to a density gradient. The solute from a band that centres at the point where its effective density is equal to that of the solvent mixture. The band has a Gaussian shape with respect to solute concentration, the half-width is inversely proportional to the molecule weight of solute. A major importance is its sensitivity to small differences in effective density among the solute species. 

The density of the liquid mixture can be determined using a pyknometer or it can be derived from a previously determined calibration curve. For the determination of densities less than unity (e.g., polyethylene), ethanol/water mixtures are suitable for densities larger than unity one may use mixtures of water with aqueous salt solutions (40% CaCl2 solution = 1.40 g/ml 72% ZnCl2 solution = 1.95 g/ml). The density gradient method, which is an elegant var-... 

Leukocytes are prepared from EDTA-blood (approximately 3-5 ml) by the density gradient method. EDTA-blood is mixed by inversion and 5 ml is slowly added to 1 ml dextran solution. The blood and dextran solution are carefully mixed so that formation of foam is avoided. The mixture is allowed to stand for 1 h. If further time for sedimentation is required, it has to be noted as it may affect the resulting enzymatic activities. The time needed for proper sedimentation depends on sample quality and should not exceed 3 h. The upper phase including the white cells is transferred to another tube and spun at 600-1000 g for 10 min. The supernatant is... 

Different grades of both of the ABS and HIPS plastics have specific gravities in the range of 1.055-1.125 g cm-1. As a result such mixtures can not be effectively separated by density gradient procedures. 

Two and Three-Parameter Simplexes (38). Three combinations of variables were examined (a) density gradient/temperature, (b) pressure gradient/temperature gradient, and (c) initial density/density gradient/temperature. Two samples were tested (i) a synthetic mixture of 6 diverse, low-to-medium molecular weight solutes of varying polarity and functionality (acetophenone, propiophenone, bicyclohexyl, biphenyl, undecylbenzene and benzophenone) and (ii) a mixture of 3 difficult-to-separate sesquiterpene lactones—glaucolide A, burrodin, and psilostachyin A. 

Crystal density is measured in a graduated cylinder by suspending the crystal in a density gradient made by mixing water-saturated organic solvents such as xylene and carbon tetrachloride. The crystal will settle through the liquid until its density matches that of the liquid mixture and then remain suspended there. Drops of salt solutions of known density are used to calibrate the gradient. 

Immunomagnetic cell separation can be used to further debulk re mixture of white blood cells obtained from the density gradient eparation and thus further enrich the suspension with rare cancer ells (see Chapter 21). Before immunochemical staining, it is usual 5 concentrate the cells onto polycarbonate membranes so that they re immobilized (see Note 8). 

The upper part of Figure 4 shows the results of the rapid density gradient centrifugation of a latex mixture of poly(styrene) and two chemically uniform co-... 

In Figure 6 the result of a rapid density gradient centrifugation is shown using this system. It deals with a graft copolymer latex of butadiene and styrene acrylonitrile. The gradient media are different mixtures of 3-butene-2-ol and ethylene glycol. 

Figure 9. Density and extinction profile in rapid density gradient centrifugation of a mixture of two latices of polybutadiene (c 20 mg L 1, N = 40.000 min 1, t — t0 = 30 min, v = 546 nm)...

Figure 6 shows the separation of the latex mixture shown in Figure 5 including an additional 0.176pm polystyrene standard. In this case, the externally prepared spin fluid/density gradient consisted of 15 ml of water and 1 ml of methanol and the disc speed was 10,450 rpm. Baseline separation and peak resolution are obtained over a decade of size range in less than 25 minutes. 

Fig. (17). Gel electrophoresis (A) and sedimentation on density gradient ultra centrifugation (B) °f anti-lactose antibodies and dissociated antibodies. Antibody (Ab), reaction mixture (R), heavy chain (H), light chain (L). ...

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