Sedimentation analysis

Sedimentation techniques such as gravity and centrifugal settling are fairly simple methods of determining the size of particles in soils and in matrices, such as paints and ceramics, where screening is not practical. For some analysis, particularly of soils, the time required to perform the analysis may take as long as 24 h. 

Knowing the particle size distribution for soils provides information about many of the soil properties, such as how much heat, water, and nutrients the soil will hold, how fast they will move through the soil, and what kind of structure, bulk density, and consistency the soil will have. The texture of the soil, how it feels, is based on the relative amounts of sand, silt, and clay present. Particles larger than 2.0 mm are called stones or gravels and are not considered soil material. Sand varies in size from 2.0 to 0.05 mm. Silt varies from 0.05 to 0.002 mm. Clays are less than 0.002 mm. 

The settling method is based on Stoke s law, which says that denser, and usually larger, particles sink farther than less dense or smaller particles. This method assumes that particles all have the same density and that they are spherical. 

In gravity settling the sample is dispersed in a liquid and then allowed to settle in a sedimentation cell. The height of the particles in the cell is then measured, or the specific gravity of the dispersing liquid is measured at different time intervals, which gives an indication of the size distribution. The hydrometer, or Bouyoucos, method is frequently used to classify the amount of sand, silt, and clay in soils. 

To perform a hydrometer test for a soil sample, a known mass of sieved ( 2 mm) soil is thoroughly mixed with a dispersing agent. It is then placed in a graduated cylinder, water is added, and the mixture is carefully agitated. A hydrometer is carefully placed in the mixture and read at 2 min, 12 min, and after 24 h. 

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Sedimentation analysis is suitable for a wide variety of materials and is used for both quaHty control and research work, such as agglomeration studies (56), and gives well-defined, relatively high resolution results. The technique has been employed in the evaluation of soils, sediments, pigments, fillers, phosphors, clays (qv), minerals, photographic haHdes, and organic particles (57,58). 

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. 

SchlMmm-. elutriating, washing, elutriated, washed, -analyse, /. analysis by elutriation sedimentation analysis, -apparat, m. elutriating apparatus, -arbeit, /. elutriation, wash ing. 

Effective dispersion of the particles is an essential prerequisite for all methods of sedimentation analysis. It is often necessary not only to stir the suspension vigorously prior to analysis, but to introduce the powder already mixed with a dispersing agent. A further agent to prevent flocculation may be needed, and it may be necessary to adjust the pH of the suspension to a suitable value determined by experiment... 

Fig. 10 Sedimentation analysis of the comparative mucoadhesiveness of a chitosan (sea cure 210+, Fa 0.11) to mucins from different parts of the stomach a Mucin source b Histogram. Adapted from [151]...

FujitaH (1962) Mathematical Theory of Sedimentation Analysis. Academic Press, New York... 

Sediment Analysis. Sediment is the most chemically and biologically active component of the aquatic environment. Benthic invertebrate and microbial life concentrate in the sediment, a natural sink for precipitated metal forms, and an excellent sorbent for many metal species. TTie extent to which potentially toxic trace element forms bind to sediment is determined by the sediment s binding intensity and capacity and various solution parameters, as well as the concentration and nature of the metal forms of interest. Under some conditions sediment analyses can readily indicate sources of discharged trace elements. 

The separation times may be adjusted according to the desired resolution. Many technical aspects of velocity sedimentation analysis are discussed in Rickwood (1992). 

Clays are manufactured from naturally occurring hydrated aluminium silicates. The particles of clays are hexagonal shaped platelets. The particle diameter quoted for these materials is not a true diameter, but only an estimate derived from sedimentation analysis. 

Delincee and Radola100 used a commercial preparation, as well as fresh tomatoes, for the preparation, purification, and characterization of tomato pectinesterase. The tomatoes were pressed and then homogenized directly with ammonium sulfate at 70% saturation. The precipitate obtained was extracted with 0.3 M phosphate and repeatedly salted out with ammonium sulfate, and the product was separated on a column of Sephadex G-75. The pattern of separation was similar to that in preceding work.50,97 A detailed study of the size properties of pectinesterase was conducted by gel-filtration and sedimentation analysis.100 By column and thin-layer gel-filtration on Sephadex G-75, the approximate molecular weight of a number of preparations of tomato pectinesterase was determined, values of 24,000 and 27,000 being obtained. A possible interaction of the... 

By use of a crude preparation obtained after the cultivation of Aspergillus niger,104 pectinesterase was purified by repeated chromatography on DEAE-cellulose, using gradient elution. The homogeneity of the product was checked by free electrophoresis, sedimentation analysis, and determination of the N-terminal amino acid (phenylalanine). 

Tokuyama Bay, Japan, received 6.6 metric tons of mercury wastes between 1952 and 1975 in wastewater from two chloralkali plants, although sediment analysis suggests that as much as 380 tons of mercury were released (Nakanishi et al. 1989). Unlike Minamata Bay, however, there were no human sicknesses reported, and the hair of residents contained 0 to 5 mg Hg/kg FW vs. 15 to 100 mg Hg/kg FW in Minamata residents. In 1970, a maximum concentration of 3.3 mg total Hg/kg FW was reported in tissues of Squilla, a crustacean. In 1973, a health safety limit was set of 0.4 mg total Hg/kg FW in edible fish and shellfish tissues with a maximum of 0.3 mg methyl-mercury/kg FW permitted at least five species of fish had more than 0.4 mg total Hg/kg FW, and fishing was prohibited. Contaminated sediments (>15 mg total Hg/kg) were removed by dredging and reclamation between 1974 and 1977. By 1979, the mercury content of all fish, except one species, was less than 0.4 mg total Hg/kg FW fishing was prohibited. By 1983, all fish and shellfish contained less than 0.4 mg Hg/kg FW and fishing was allowed (Nakanishi et al. 1989). 

A sample may be characterized by the determination of a number of different analytes. For example, a hydrocarbon mixture can be analysed by use of a series of UV absorption peaks. Alternatively, in a sediment sample a range of trace metals may be determined. Collectively, these data represent patterns characteristic of the samples, and similar samples will have similar patterns. Results may be compared by vectorial presentation of the variables, when the variables for similar samples will form clusters. Hence the term cluster analysis. Where only two variables are studied, clusters are readily recognized in a two-dimensional graphical presentation. For more complex systems with more variables, i.e. //, the clusters will be in -dimensional space. Principal component analysis (PCA) explores the interdependence of pairs of variables in order to reduce the number to certain principal components. A practical example could be drawn from the sediment analysis mentioned above. Trace metals are often attached to sediment particles by sorption on to the hydrous oxides of Al, Fe and Mn that are present. The Al content could be a principal component to which the other metal contents are related. Factor analysis is a more sophisticated form of principal component analysis. 

The presence of organic compounds in river and oceanic sediments is due, in part, to manmade pollution and monitoring the levels of these substances in the sediment and sediment cores provides an indication of the time dependence of their concentration over large time spans. Contamination of sediments is found not only in rivers but also in estuarine and oceanic sediments and thus sediment analysis provides a means of tracking organic from their source through the ecosystem. 

This technique has found limited applications in sediment analysis and has been applied to the determination of aromatic hydrocarbons in saline sediments and mixtures of organics in non-saline sediments. 

This technique has found very limited applications in soil and sediment analysis and is particularly useful when routine automated analyses at the mg L 1 level of large numbers of samples is required. The technique has been applied to the determination of total phosphorus, total organic carbon and total nitrogen in soils, total organic carbon in non-saline sediments and total sulphur in saline sediments. 

Keith et al. [36] and Reijnders et al. [37] reviewed applications of gas chromatography-mass spectrometry to sediment analysis. Lopez-Avila et al. [38] investigated the efficiency of dichloromethane extraction procedures for the isolation of organic compounds from sediments prior to gas chromatography-mass spectrometry. The compounds investigated were the 51 priority pollutants listed by the Environmental Protection Agency, USA. 

A complete particle-size analysis can require the use of various analysis technologies. A microscopic examination may be performed before the sieve analysis, which in turn can be followed by a sedimentation analysis or the recording and the evaluation of a diffraction pattern. 

An optical measuring system is used in sedimentation analysis, whereby a concentrated beam of light is deflected horizontally through the lower section of a measuring vessel onto a photoelectric cell. The amount of light absorbed by the sedimenting particles decreases with time as the... 

Coulter counter analysis Sieve analysis Sedimentation analysis Time of flight measurements (Scanning electron) microscopy... 

Figure 6 shows the results of a sedimentation analysis. Comparison with a sample of a functionality of f = 0.7 allows an unambiguous assignment of the remarkably sharp peak in the upper trace as resulting from the multimers. The narrow width of the signal and the fast sedimentation is typical of compact sphere-like molecules having a narrow molecular weight distribution. 

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