Ultracentrifuge optics

The reactants are then mixed in various proportions, and the sedimentation ratio (scompiex/smucin)—the ratio of the sedimentation coefficient of the complex to that of the pure mucin itself—is used as the measure for mucoad-hesion. The ultra-violet absorption optics on the XL-A or XL-1 ultracentrifuge have been used as the main optical detection system. Although the polysaccharide is generally invisible in the near UV ( 280 nm), at the concentrations normally employed the mucin—in uncomplexed and complexed form—is detectable. 

Winzor and coworkers have employed measurements of the Donnan distribution of small ions in dialysis equilibrium [14] to reinforce earlier evidence of charge-screening effects in polysaccharide anions [164,165]. These researchers used the absorption optical system of a Beckman XL-1 ultracentrifuge to monitor the distribution of ions in polysaccharide solutions... 

Techniques which seem less suitable for routine size analysis are (1) analytical ultracentrifugation combined with a Schlieren optical system (Mason and Huang, 1978 Weder and Zumbuehl, 1984) (2) the sedimentation field flow fractionation (SFFF) technique to separate heterogeneous dispersions (e.g., Kirkland et al., 1982). 

The cell is fitted with windows, and the concentration of polymer along its length is determined by optical methods which are based on measurements of refractive index of absorption solvents to be used for ultracentrifugation experiments must be chosen for difference from the polymer in both density and refractive index. An effort be made to avoid mixed solvents. Low solvent viscosity is also desirable. 

Transport Analysis Using the Ultracentrifuge Schlieren Optics... 

The use of absorption optics with the ultracentrifuge has allowed us to monitor the rapid transport of PVP in the standard PVP/dextran system as a function of g. It was demonstrated that while the rate of the PVP transport increases with increasing g acting on the system, the rate is rather insensitive to the magnitude of the gravitational force. We found 51) that the linear time rate of the transport varies as g°19. Note, however, that although rapid PVP transport has been found at various values of g, we cannot be sure whether structured flows exist. 

FIG. 2.6 Schematic of optical systems in the Spinco Model E Ultracentrifuge (Beckman Instruments, Inc., Spinco Division, Palo Alto, CA). 

The schlieren system of optics is an analytical method that is particularly well suited to following the location of a chemical boundary with time. It is routinely employed in ultracentrifuges and also in electrophoresis experiments, as we see in Chapter 12. Schlieren optics produces an effect that depends on the way the refractive index varies with position, that is, the refractive index gradient rather than on the refractive index itself. Therefore, the schlieren effect is the same at all locations along the axis of sedimentation, except at any place where the refractive index is changing. In such a region, it will produce an optical effect that is proportional to the refractive index gradient. The boundary between two layers is thus per-... 

FIG. 2.7 Location of the boundary for particles settling in an ultracentrifuge (a) concentration profile and (b) derivative profile as revealed by schlieren optics. (Redrawn with permission of P. C. Hiemenz, Polymer Chemistry The Basic Concepts, Marcel Dekker, New York, 1984.)... 

The method of equilibrium ultracentrifugation described by Yphantis (28) was used in these studies. A double-sector centerpiece with two 2 1/2° sectors 12 mm. in length was used with standard Schlieren optics. Apparent molecular weights, M, were determined from the equation ... 

Figure 3-7 The scanning absorption optical system of the Beckman Optima XL-A ultracentrifuge. Courtesy of Beckman Coulter.

Ultracentrifugation 108,109 Ultracentrifuge 100 analytical 108 optical system, figure 109 Ultrafiltration 100 Ultrasensitive responses 567 Ultrasonic sound 468 UMP (Uridine5-phosphate) 200, 200s,203 Unimolecular processes 457 Uniporters 414 Units, International System 2 Unsatisfied ends of hydrogen bonded chains 64... 

Here h is the thickness of the ultracentrifuge centerpiece (usually 12 mm), n — n0 is the refractive index difference between the solution (n) and the solvent (n0), and A is the wavelength of light used (generally 546 /a). Thus with the Rayleigh optical system one can obtain n, which can be expressed as... 

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