Measurement sedimentation methods

Methods for determining time-weighted concentrations while taking the sample Methods of making in situ measurements Laboratory methods Methods using devices that can read the amount/concentration of analyte directly Methods with previously prepared samples and the amount/ concentration of analyte calculated from laboratory measurements Sedimentation methods... 

In general, it appears that the Micromerograph, provided that frequent calibration checks are performed, is a good, reproducible instrument for size measurement. The operator time involved is less than with most other methods, and the calcns are not complicated. As in all sedimentation methods, only when the sample particles are spherical does the Stokes diameter that is measured become a measure of absolute particle size. Microscopic examination should be used to check on particle shape and the effect of deagglomeration... 

Various techniques and equipment are available for the measurement of particle size, shape, and volume. These include for microscopy, sieve analysis, sedimentation methods, photon correlation spectroscopy, and the Coulter counter or other electrical sensing devices. The specific surface area of original drug powders can also be assessed using gas adsorption or gas permeability techniques. It should be noted that most particle size measurements are not truly direct. Because the type of equipment used yields different equivalent spherical diameter, which are based on totally different principles, the particle size obtained from one method may or may not be compared with those obtained from other methods. 

Viscosity of polyamic acid. measured using sedimentation method in NMP. ins insoluble s soluble ps partially soluble. ... 

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

In continuous technological processes direct measurement of products masses is difficult. The recoveries are usually estimated by determination of the fraction content in separated products. This may be done by analyzing their probes, e.g. by sieving, sedimentation method etc. Using the fraction contents, one can estimate the recoveries of coarse and fine fractions by the following respective expressions rjc = Cc(C0 - Cf)/[C0(Cc - Cf)], m = Ff(F0 - Fc)/[F0(Ff — Ec)]. Their average gives total separation efficiency rjaY... 

Central to any investigation of particle swelling is the use of a reliable method of measuring the size of the particles undergoing expansion. A sedimentation method was described previously (5) which can be used to explore the expansion characteristics of carboxylic emulsion polymers. In the present report, we present a comparison of sedimentation results with those obtained with two... 

Surface layers (adsorbed, solvated, ionic) are of considerable importance in controlling the stability and rheological properties of colloidal systems. Sedimentation methods have proven effective in the measurement of adsorbed layer thickness using equations similar to Equation 1 when the density of the layer could be estimated ( 7,8). The equation can be considerably simplified if the density... 

Viscometric particle swelling experiments were carried out with a Cannon-Ubbelohde shear-dilution viscometer thermostated at 30 + 0.05°C. The shear rate was approximately 2000 sec-1 with flow times determined to + 0.1 sec. As in the sedimentation method, the model latexes were diluted with distilled water to a concentration of approximately 1 percent. Individual samples were adjusted with sodium hydroxide to various pH values and allowed to equilibrate at least 24 hours before measuring the viscosity. 

In essence, the sedimentation method gives a ratio of the hydrodynamic radius at a given pH to the hydrodynamic radius of the same particles at a reference pH. It is not an absolute method and requires an independent absolute measurement of particle radius. 

The expansion behavior of carboxylic latex particles can be studied by several methods (10). The present comparison was made using a sedimentation method which involved the measurement of particle sedimentation rates in an ultracentrifuge at various degrees of neutralization. Assuming the change in particle volume is equal to the volume of water absorbed, an expanded particle settles slower, as its density decreases, according to the equation ... 

The sedimentation methods are normally used to measure the size of particles in a liquid medium because of the relatively high viscosity effects in liquids compared to gases. The particles in a liquid may become solvated, yielding increased weight and volume of the particle. Meanwhile, the buoyant effect on the solvated particle in the surrounding medium... 

The method selected depends upon the kind of material to be measured. If particles are confined to narrow limits of size, screens or microscopic methods of direct measurement may be used. When particles are distributed over a wide range of sizes we must choose indirect methods such as sedimentation or centrifuging. There is no simple method of measurement in either case, and the results are not always susceptible of interpretation unless the composition of the material is known. This will be even more evident when we consider sedimentation methods applied to particles varying widely not only in size but also in density. 

The sign in the present instance is negative if we regard q as the number of particles greater than a given diameter d. We are not concerned with the form of either q or F(d) for the time being. The technique involved requires only that we determine the size-distribution graphically. With sedimentation methods the form of frequency function is important mathematically only in so far as it explains the relationships of the variables measured. 

The microscopic method was used in only one set of experiments, viz., for a material whose median effective diameter was 25 /x. Good agreement was found between pipette, hydrometer, and microscopic methods for sizes ranging from 25 to the upper limit of the experiment, 100 ix. Below 25 ix, both sedimentation methods gave similar results, but there was a marked difference with the microscopic method. Thus, at 10 ix, the percent found undersize by the sedimentation methods was 25 percent and that found undersize by the microscopic method was 12 percent. This difference can be attributed in part to difficulties in preparing samples for measurement, but undoubtedly the failure to commute shape factors can be regarded as the chief source of divergencies. 

Measurements of sedimentation behaviour of polymer molecule in solution can provide a consideratble amount of information, e.g., hydrodynamic volume, average molar masses and even some indication of molar mass distribution. Such measurements have been extensively used to characterise biologically-active polymers which often exist in solution as compact spheroids or rigid rods. However, sedimentation methods are rarely used to study synthetic polymers and so will be given only brief non-theoretical consideration here. 

Eyre, B. D., Rysgaard, S., Dalsgaard, T., and Christensen, P. B. (2002). Comparison ofisotope pairing and N2 Ar methods for measuring sediment denitrification-Assumptions, modifications, and imph-cations. Estuaries 25, 1077—1087. 

The solution of the integral for measuring the concentration at constant position over time is only approximately possible. A common way uses Kamack s equation [Kamack, Br. J. Appll. Phys., 5, 1962-1968 (1972)] as recommend by ISO 13318 Part 1 Determination of Particle Size by Centrifugal Liquid Sedimentation Methods). 

The sedimentation method depends on measuring the sedimentation coefficient (by ultracentrifugation) of the particles, SJ (extrapolated to zero concentration), in the presence of the polymer layer [34]. Assuming that the particles obey Stokes law, SJ is given by the expression ... 

There is a wide variety of methods for particle size measurement which measure different types of particle size. When selecting a method, it is best to take one that measures the type of size which is most relevant to the property or the process which is under study. Thus, for example, in powder elutriation, pneumatic conveying or gas cleaning, it is most relevant to use one of the sedimentation methods which measure the Stokes diameter, i.e. the diameter of a sphere of the same density as the particle itself, which would fall in the gas at the same velocity as the real particle (assuming Stokes law). In flow through packed or fluidized beds, on the other hand, it is the surface-volume diameter (or diameter... 

Independent measurements of sizes of spherical particles by diffusional methods (r D ]), and by sedimentation methods (r S I/2) usually yield results that are in good agreement with each other. 

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