Liquid-Solid General Selection

Effect of particle diameter and solid concentration on the choice For particle diameter greater than 1000 (jm and soUd concentration 3%, use screens, Section 5.7. 

For particle diameter less than 2 cm and 5 pm and solid concentration 1 to 50%, consider settlers, filters or centrifuges. 

For particle diameter less than 300 pm and solid feed concentration 0.01 to 20%, consider thickeners. Section 5.10. 

For particle diameter greater than 20 pm and solid feed concentration greater than 50%, consider dryers. Section 5.6. 

For particle diameter 0.01 to 150 pm, consider deep bed filter. Section 5.14 or dissolved air flotation. Section 5.16. 

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Solubilizing all or part of a sample matrix by contacting with liquids is one of the most widely used sample preparation techniques for gases, vapors, liquids or solids. Additional selectivity is possible by distributing the sample between pairs of immiscible liquids in which the analyte and its matrix have different solubilities. Equipment requirements are generally very simple for solvent extraction techniques. Table 8.2 [4,10], and solutions are easy to manipulate, convenient to inject into chromatographic instruments, and even small volumes of liquids can be measured accurately. Solids can be recovered from volatile solvents by evaporation. Since relatively large solvent volumes are used in most extraction procedures, solvent impurities, contaminants, etc., are always a common cause for concern [65,66]. 

Levels of drug and/or its metabolite have to be determined in plasma samples collected during the course of a toxicity study in order to evaluate the toxicokinetics of that compound. The UV absorption properties of the compound are used to determine the compound of interest. Since many of the endogenous compounds also show absorption in that wavelength range, a tailored sample work-up has to provide additional selectivity for the compound of interest. In addition, the plasma proteins have to be removed by the work-up in order to avoid blocking of the HPLC columns. Three principles are generally applied to remove the proteins from the sample Protein precipitation, liquid/liquid extraction and liquid/solid extraction. 

The selection of an extraction procedure depends primarily on the class of compounds of interest as well as the type and physical state of the sample. Liquid samples generally do not require extraction prior to analysis however liquid-liquid extraction may be performed to isolate a certain class of compounds. Extraction of antioxidants from solid plant materials is most commonly done using aqueous mixtures of organic solvents. This is based on the principle that, upon extraction. 

Therefore, in liquid-solid chromatographic systems selectivity in a separation is determined by the mobile phase solvent strength and interaction with the adsorbent. The general selectivity triangle... 

Liquid-liquid extraction is a process by which one or more components of a mixture, usually in water, are selectively transferred to another, usually organic liquid. Liquid-solid extraction involves the use of a liquid to selectively remove components from a solid. The majority of laboratory scale extractions are batch extractions, involving separatory funnels. The theory and general techniques are discussed in Chapter 9. 

The oil shale reactor selection can now be generalized to the general case of multiphase reactors (gas-liquid, gas-solid, gas-liquid-solid,... 

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