Sedimentation measurements

Thus the quantity on the left evaluated for a series of polymer fractions differing only in chain length should be independent of M. Results shown in Table XLII for fractions of poly-(methyl methacry-late) and of polyisobutylene covering unusually wide ranges confirm this prediction within experimental error. It is borne out also by less extensive results of sedimentation measurements on several other systems. Introduction of the values of v, p, and rjo enables... 

Diffusion and sedimentation measurements on dilute solutions of flexible chain molecules could be used to determine the molecular extension or the expansion factor a. However, the same information may be obtained with greater precision and with far less labor from viscosity measurements alone. For anisometric particles such as are common among proteins, on the other hand, sedimentation velocity measurements used in conjunction with the intrinsic viscosity may yield important information on the effective particle size and shape. ... 

Miner et al. [50] prepared monodispersed AuPt and PdPt alloys by simultaneous reduction of the corresponding salt mixtures at various molar ratios. They confirmed that AuPt alloys are formed at any atomic ratio, even if the two metals show a broad miscibility gap between 2 and 85wt% Au [51]. The homogeneous character of the various AuPt alloys was proven by means of optical spectra, sedimentation measurements, and electron microscopy. 

Absolute methods end group analysis, membrane osmometry, vapor pressure osmometry, static light scattering, mass spectrometry, sedimentation measurements. 

Coil dimensions Static light scattering, sedimentation measurements, small angle X-ray, solution viscosity... 

So far, this method appears not to have been used as such, but sedimentation measurements have been combined with those of other kinds. Thus Moore and co-workers 136) assumed Eq. (9.3) and also that g =gi following Thurmond and Zimm (33) these assumptions led to the relation ... 

K-casein aggregates in aqueous medium are more complicated than those of p-casein, being composed of star-like sub-micelles, where each submicelle contains nine K-casein chains and the total degree of association may reach about 140 (Thum el al., 1987a). Payens and Vreeman (1982) used sedimentation measurements to infer a critical micelle concentration for K-casein of 0.5 mg/ml. 

Payens, T.A.J., Brinkhuis, J.A., van Markwijk, B.W. (1969). Self-association in nonideal systems. Combined light scattering and sedimentation measurements in p-casein solutions. Biochimica etBiophysica Acta, 175, 434 137. 

A basic limitation of all these methods is the narrow range of particle sizes that can be investigated by sedimentation under gravity. Therefore, we turn next to a consideration of centrifugation, particularly the ultracentrifuge, as a means of extending the applicability of sedimentation measurements. 

Regarding FAAS, only a study by Flores et al. [74] employed PLS to quantify Cd in marine and river sediments measured by direct solid sampling FAAS. 

Figure 28-1 Depth profile of nitrate in sediment from freshwater Lake Spbygard in Denmark. A similar profile was observed in saltwater sediment. Measurements were made with a biosensor containing live bacteria that convert N03 into N20, which was then measured amperometrically by reduction at a silver cathode. [From l h. Larsen, i Kjosr. and N. P. Revsbech. A Microscale NO Biosensor for Environmental Applications," Anal- Chem. 1997, <59.3527.]... 

Revsbech, N.P. and 3j8rgensen, B.B., 1981. Primary production of microalgae in sediments measured by oxygen microprofile, H 1 003" fixation, and oxygen exchange methods. Limnol. Oceanogr., 26 717-730. 

This relationship is commonly used in environmental fate models to predict aqueous concentrations from sediment measurements by substituting the equilibrium expression for Kp and rearranging to solve for Cw ... 

Calculate the relative molecular mass of the spread protein and compare your answer with a value of 68000 as determined from sedimentation measurements. 

Sediment measured t,/2 = 450 d at 25°C, based on neutral and base-catalyzed hydrolysis rates studied in pure water and in barely saturated subsurface sediment at 25-60°C (Haag Mill 1988). 

It is easier experimentally to determine 5 than to perform an equilibrium sedimentation measurement, but, because we are interested in the molar mass and the density increment, D has to be determined independently. 

Rysgaard, S., Risgaard-Petersen, N., Nielsen, L.P., and Revsbech, N.P. (1993) Nitrification and denitrification in lake and estuarine sediments measured by the 15 N dilution technique and isotope pairing. Appl. Environ. Microbiol. 59 2093-2098. 

Sprensen, J. (1978) Denitrification rates in a marine sediment measured by the acetylene inhibition technique. Appl. Environ. Microbiol. 36 139-143. 

The first physico-chemical determination appears to be that of Kekwick.116 He examined in the ultracentrifuge the material prepared from ovarian cyst fluid which showed blood-group A specificity.117 This product was electrophoretically homogeneous and only one component was apparent in the sedimentation measurements. The complex was moderately polydisperse and possessed a highly asymmetric shape (f/fo = 3.2). The values of the sedimentation and diffusion constants, interpolated graphically at a given concentration, corresponded to a mean molecular weight of 260,000... 

Gibson QH, Hoffman BM, Crepeau RJH, Edelstein SJ, Bull C. Manganese hemoglobin Allosteric effects in stopped flow flash photolysis and sedimentation measurements. Biochem Biophys Res Commun 1974 59 146. 

Centrifugation data from measurements with an analytical ultracentrifuge are useful for characterizing glycoenzymes. Pure gly-coenzymes yield symmetrical patterns when examined by this procedure. Sedimentation measurements can be made at several concentrations of the enzyme, and a number of physical constants characteristic of the molecule can be calculated from these data. On the basis of such measurements and calculations, it was determined that chloroperoxidase, which contains carbohydrate, is homogeneous with respect to molecular size,21 and it was concluded that the carbohydrate component in the preparation of chloroperoxidase studied is chemically linked to the protein. 

In addition, more complex exponent averages can be obtained (e.g., by dilute Solution viscometry and sedimentation measurements). 

The original Acoustosizer used a single frequency whereas a later development has a range of 13 frequencies between 0.3 and 13 MHz. This allows the measurement of the dynamic mobility spectrum and the determination of the zeta potential and particle size. In order to invert the mobility spectrum into a size distribution a log-normal distribution of particle size is assumed. A comparison with photon correlation spectroscopy for determining particle size and laser Doppler anemometry for particle charge eonfirmed the results using ACS [266]. These and additional sedimentation measurements confirmed that changes in particle size and zeta potential due to dilution effects are likely to occur in aqueous and non-stabilized systems. 

Luther, G. W., Brendel, P. J., Lewis, B. L., Sundby, B., Lefrancois, L., Silverberg, N., and Nuzzio, D. B. (1998). Oxygen, manganese, iron, iodide, and sulfate distributions in pore waters of marine sediments measured simultaneously with a solid state voltammetric electrode. Limnol. 

Figure 22 Adsorption of trace metals by the Meuse River bottom sediments measured data in NaN03 0.01 M and interpretation (curves) in terms of adsorption.

---