Probe sedimentation

Laurent and Pietmszkiewicz examine the sedimentation of bovine serum albumin, yellow turnip vims, and four diameters of polystyrene latex spheres through aqueous 0.14 and 1.7 MDa hyaluronic acid(4). They report that 

Here A and B are substance-dependent constants, with A in the range 1-1.6 and B increasing more than 20-fold with a c. 60-fold increase in probe radius. In the original papers v was assumed to be constant at v = 0.5. The matrix concentration was no larger than 7 g/1, which was enough to reduce s of the larger particles (latex spheres, radii 88-365 nm) by 2-3 orders of magnitude. Limited measurements 

Laurent, et al. examine ten biomacromolecules and colloidal silica in 1.7 MDa hyaluronic acid(5). For all probe particles, s had a stretched-exponential dependence on matrix c, with v = 0.5. 5 was independent of the centrifugal acceleration, i.e., experiments were in a linear domain in which solution viscoelastic properties were not evident. Contrast is to be made with the electrophoretic mobility, as discussed in the next chapter, in which one can enter a nonlinear domain in which particle mobility depends on the applied field E. The constant B was found, to good accuracy, to be linear in the particle radius, except for the very largest spheres. Laurent, et al. also measured the diffusion coefficients D of four smaller probes in the same polymer solutions. Within experimental error, s/D was independent of matrix concentration. 

Laurent, et al. specifically promise a subsequent paper in which. ..it will be shown that this sieving ejfect can be used for the separation of various compounds that would otherwise sediment together in the ultracentrifuge... 5). The polymer solution sieving effect is the differential effect of polymer solutions on the sedimentation rate of particles of different size, as reflected in the dependence of B on particle radius. This proposal to use polymer solutions as a path to biochemical separations has come to fruition a half-century later in the use of polymer solutions as support media in electrophoresis. 

(21) and Ye, et al.(22,23) report sedimentation of 4.0 nm surfactant-coated calcium carbonate particles through monodisperse hydrogenated polyiso-prenes in decane. Unmodified hydrogenated polyisoprene is nonabsorbing to the coated carbonate spheres. Addition of an end-terminal amino group yields an 

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Modem discussions of probe sedimentation are traced to the seminal study of Langevin and Rondelez(3). They determined s of bovine serum albumin, bushy stunt vims, eggplant mosaic virus, ludox, and polystyrene latex spheres in solutions of polyethylene oxide. Langevin and Rondelez proposed a stretched-exponential dependence of s on c, M, and R, namely... 

Koenderink, et al. examined the motion of perfluorinated hydrocarbon spheres through xanthan solutions(72). Depolarized QELSS spectra were measured at a series of angles and fitted to second-order cumulant expansions. The spheres had radius 92.5 nm the xanthan molecular weight was 4 MDa. Koenderink, et al. measured solution viscosity, shear thinning, storage and loss moduli, translational and rotational diffusion coefficients Dp and Dr of the probes, and probe sedimentation coefficient s, and made an extensive and systematic comparison... 

In ternary mixtures at small matrix concentration, larger probes sediment more rapidly. However, with increasing matrix concentration the sedimentation coefficient of a larger probe decreases more rapidly than does the sedimentation coefficient of a smaller probe, so at large c large probes sediment more slowly than smaller probes. The a of Eq. 15.1 increases approximately linearly with the hydrodynamic radius of the probe. The a also increases with matrix molecular weight, even when the matrix polymer is much larger than the probes. Indeed, a polymer matrix solution can hinder probe sedimentation when the matrix sediments more rapidly than the probe does. 

An experimental problem is to obtain adequate dispersion of the particles before sedimentation analysis. For powders that are difficult to disperse the addition of dispersing agents is necessary, together with mtrasonic probing. It is essential to examine a saiTmle of the dispersion under a microscope to ensure that the sample is fully dispersed. 

Figure 8 Chemiluminescent (A and B) and bioluminescent (C) detections for immobilized hybridizations of PCR product. Dg, digoxigenin Bt, biotin Ad, avidin. Procedure A [30] Biotin moiety is incorporated into PCR products during the amplification reaction, using one 5 -biotinylated primer. The product is hybridized with a Dg-labeled probe and is immobilized on streptavidin-coated magnetic beads. This capture reaction is carried out for 30 min at 37°C. A permanent magnet is used to sediment the beads during washing to remove unbound DNA. By incubation with the washed beads for 45 min at 37°C, anti-Dg antibody conjugated to HRP enzyme is bound to the Dg-labeled probe, and luminol reaction is performed for CL detection. Procedure B [31] Wells of apolystyrene microtiter plate are activated with l-ethyl-3-(3-dimethylaminopropyl)-carbodiimide, and then coated with a labeled cDNA probe complementary to an internal region of the target DNA.

Possible environmental applications of NIR probes include the measurement of trace amounts of metal pollutants in surface and ground waters and water saturated soils and sediments and the detection of lead, chromium, and other heavy metal ions for efforts in pollution control. Also OFCD could assist in the determination of caustic soda and chlorine contents in wastewaters. 

Figure 4. Comparative detection of 4-chlorobiphenyl catabolic gene abundance by blot hybridization of pSSSO plasmid DNA probe to target DNA extracted from sediments. A B spatially separated sediments C control self hybridizations. (Units A B, ug total DNA C ng of probe DNA.)...

In sediment and soil samples, the isomers of cresol are determined by transferring a small portion of the solid sample (1 g) to a vial and adding methylene chloride. The contaminants are extracted from the sample with the aid of an ultrasonic probe. The methylene chloride extract is filtered, concentrated, and subjected to GC/MS analysis for quantitation. 

Measurement of Deposit. Common methods used to measure sediments are manual testing, sedimentation balance, radioactive methods, dipping of bodies, and probe tools. 

High-resolution compositional measurements are possible through use of a variety of microanalytical methods. Ideally, these should be non-destructive, can be targeted on small areas of sample, and have low minimum detection limits. Electron-probe X-ray microanalysis (EPXMA) and proton-induced X-ray emission (PIXE) techniques have both been used successfully on archaeological sediment thin sections (19, 20). Both techniques yield elemental composition data for a range of elements. EPXMA has the advantage of being nondestructive, whereas PIXE when used on thin-section samples is typically destructive conversely the detection limit for PIXE is lower than EPXMA. 

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