Homogeneous separation

Separation of the different phases of a heterogeneous mixture should be carried out before homogeneous separation, taking advantage of what already exists. Phase separation tends to be easier and... 

All of the systems discussed so far involve homogeneous separation, that is, a single-phase liquid throughout. Consider now distillation systems involving two-liquid phases. 

Fresh plant materials, Allium sativum (bulb and green), Allium cepa rubra (bulb) wA Allium cepa (bulb and green), were homogenized separately in physiological saline (pH 7.4). Homogenates were centrifuged at 10,000 g at 4°C for 30 min. 

The homogeneous separated fractions, with the exception of hydrocarbons, are derivatized by silylation in order to reduce their polarity, and analysed in capillary gas chromatography. 

Immunochemical methods for low molecular weight (<1000 D) environmental compounds, such as pesticides, nitro aromatics, and PAHs (polycyclic aromatic hydrocarbons) have been developed since more than 25 years (e.g. Hammock and Mumma, 1980 Hammock et al., 1990 Dankwardt, 2000). The most common method is the immunoassay, which is either carried out with (heterogeneous) or without (homogenous) separation steps. Heterogeneous formats that use microtitre plates, plastic tubes and/or membranes as solid supports are more commonly used. 

This is usually the first choice for homogeneous separation. 

For particle diameter <2 cm and >5 pm and solid concenttation 1 to 50%, consider settlers, filters, or centrifuges. For particle diameter <300 pm and solid feed concentration 0.01 to 20%, consider thickeners. Section 16.11.5.9. For particle diameter >20 pm and solid feed concentration greater than 50%, consider dryers. Section 16.11.5.5. For particle diameter 0.01 to 150 pm, consider deep bed filter. Section 16.11.5.13, or dissolved air flotation. Section 16.11.5.15. For particle diameter 0.6 to 40 pm and solids concenttation <0.1%, consider homogeneous separation via ultraflltration, Section 16.11.4.22. For particle diameters from 0.8 to 20 pm, consider using a filter aid to precoat on the filter medium. For example, use diatomous earth or perlite. A fine filter... 

Reservoir geochemistry often begins with the premise that petroleum in a given pool is so well mixed that the composition is more or less homogeneous. Separate compartments are invoked whenever the compositions at different locations differ by more than accepted amounts, especially if the reservoir pressures also imply a lack of communication. 

Soient S un pr6sch ma noetherien, G un S-pr6sch6ma commu-tatif, plat et de presentation finie sur S et X un G-espace homogene separe sur S tel que = (o>pr2) soit affine. Alors il existe un ou-vert U de S et un sous-S-groupe F de G plat et de presentation finie sur S tels que le faisceau quotient de G par F dans (Sch/S) soit representable sur U et que Xy soit un (G/F)jj-espace homogSne principal sur U. ... 

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