Screening solid mixtures

Filtration is the separation of a fluid-solids mixture involving passage of most of the fluidthrough a porous barrier which retains most of the solid particulates contained in the mixture. This subsec tion deals only with the filtration of solids from liquids gas filtration is treated in Sec. 17. Filtration is the term for the unit operation. A filter is a piece of unit-operations equipment by which filtration is performed. The filter medium or septum is the barrier that lets the liquid pass while retaining most of the solids it may be a screen, cloth, paper, or bed of solids. The hquid that passes through the filter medium is called the filtrate. 

Functional molecules can also be immobiUzed by preparing a paste containing these molecules together with binders and conductive solid particles. The paste is used to coat a solid surface. Carbon pastes prepared in this way are frequently applied in electrochemical sensors. A special variant is the use of a conductive organic salt substituting carbon particles as well as the binder. Sensors with pastes are well suited for laboratory use, in particular if tests must be conducted. When used in commercial applications, commonly the paste is substituted by a screen-printed mixture of similar composition. Screen-printing inks generally also contain binders, conductive particles and dissolved functional substances. 

The analytical cut size Tp is defined such that a hypothetical and ideal screen having this size opening will give from the feed solid mixture the same value of total efficiency Et as the actual separator. In terms of the feed particle size distribution fimction, ly(rp). 

For solution-phase libraries that are composed of mixtures of compounds, the difficulty of analysis escalates with increasing numbers of compounds. Typically, large mixtures of compounds are not analyzed before screening, whereas small ones may be analyzed for reaction completeness using mass spectrometry, HPLC, NMR, or combinations thereof. The identification and analysis of active compounds from these mixtures is painstakingly tedious, and often complete characterization is possible only after deconvolution procedures and resynthesis of the active compound. For solid-phase libraries, the methods currendy developed are discussed below. 

Techniques to screen individual compounds or mixtures in solution or still attached to the solid support are available. The main advantage... 

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