Solid-phase extraction multistage

See also Atomic Absorption Spectrometry Interferences and Background Correction. Atomic Emission Spectrometry Principles and Instrumentation Interferences and Background Correction Flame Photometry Inductively Coupled Plasma Microwave-Induced Plasma. Atomic Mass Spectrometry Inductively Coupled Plasma Laser Microprobe. Countercurrent Chromatography Solvent Extraction with a Helical Column. Derivatization of Analytes. Elemental Speciation Overview Practicalities and Instrumentation. Extraction Solvent Extraction Principles Solvent Extraction Multistage Countercurrent Distribution Microwave-Assisted Solvent Extraction Pressurized Fluid Extraction Solid-Phase Extraction Solid-Phase Microextraction. Gas Chromatography Ovenriew. Isotope Dilution Analysis. Liquid Chromatography Ovenriew. 

A process flow sheet for countercurrent multistage leaching is shown in Fig. 12.10-1 and is similar to Fig. 12.7-1 for liquid-liquid extraction. The ideal stages are numbered in the direction of the solids or underflow stream. The solvent (C)-solute (A) phase or V phase is the liquid phase that overflows continuously from stage to stage countercurrently to the solid phase, and it dissolves solute as it moves along. The slurry phase L composed of inert solids (B) and a liquid phase of A and C is the continuous underflow from each stage. Note that the composition of the V phase is denoted by x and the composition of the L phase by y, which is the reverse of that for liquid-liquid extraction. 

Solids may be processed continuously or semicontinuously by pumping slurries or by using lock hoppers. An example is the separation of insoluble polymers by floatation with a variable-density SCF. For liquid feeds, multistage separation may be achieved by continuous counter-current extraction, much like conventional liquid-hquid extraction. The final produces may be recovered from the extract phase by a depressurization, a temperature change, or by conventional distillation. 

The partitioning of a substance between two liquid phases (multistage partitioning, partition chromatography) and the extraction of solids require similar properties of a solvent [50-55]. When a substance has to be partitioned, a solvent system with limited miscibility of the components is required in order that the substance dissolves to a different extent in the two phases. The greater the chemical differences between any two solvents, the more limited their miscibility. Other requirements that the solvent system must fulfil are, inter alia, a favorable partition coefficient (the average partition coefficient of the component mixture should be between ca. 0.2 and 5), as high a separation... 

These operations are all similar in that the mixture to be separated is brou t into contact with another insoluble phase, the adsorbent solid, and the unequal distribution of the ori al constituents between the adsorbed phase on the solid surface and the bulk of the fluid then permits a s aration to be made. All the techniques previously found valuable in the contact of insoluble fluids are useful in adsorption. Thus we have batchwise single-stage and continuous multistage separations and separations analogous to countercurrent absorption and stripping in the field of gas-liquid contact and to rectification and extraction with the use of reflux. In addition, the rigidity and immobility of a bed of solid... 

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