Solid phase techniques separation method

The movement of the analyte is an essential feature of separation techniques and it is possible to define in general terms the forces that cause such movement (Figure 3.1). If a force is applied to a molecule, its movement will be impeded by a retarding force of some sort. This may be as simple as the frictional effect of moving past the solvent molecules or it may be the effect of adsorption to a solid phase. In many methods the strength of the force used is not important but the variations in the resulting net force for different molecules provide the basis for the separation. In some cases, however, the intensity of the force applied is important and in ultracentrifugal techniques not only can separation be achieved but various physical constants for the molecule can also be determined, e.g. relative molecular mass or diffusion coefficient. 

Analytical separations may be classified in three ways by the physical state of the mobile phase and stationary phase by the method of contact between the mobile phase and stationary phase or by the chemical or physical mechanism responsible for separating the sample s constituents. The mobile phase is usually a liquid or a gas, and the stationary phase, when present, is a solid or a liquid film coated on a solid surface. Chromatographic techniques are often named by listing the type of mobile phase, followed by the type of stationary phase. Thus, in gas-liquid chromatography the mobile phase is a gas and the stationary phase is a liquid. If only one phase is indicated, as in gas chromatography, it is assumed to be the mobile phase. 

A method which uses supercritical fluid/solid phase extraction/supercritical fluid chromatography (SE/SPE/SEC) has been developed for the analysis of trace constituents in complex matrices (67). By using this technique, extraction and clean-up are accomplished in one step using unmodified SC CO2. This step is monitored by a photodiode-array detector which allows fractionation. Eigure 10.14 shows a schematic representation of the SE/SPE/SEC set-up. This system allowed selective retention of the sample matrices while eluting and depositing the analytes of interest in the cryogenic trap. Application to the analysis of pesticides from lipid sample matrices have been reported. In this case, the lipids were completely separated from the pesticides. 

Four types of techniques for separating the bound fraction P Q from the reagent mixture are in common usage, loosely termed double antibody, solid phase, charcoal adsorption and solution precipitation. The first type is used with radioimmunoassay methods specifically, while the other three types can be used with both radioassay and radioimmunoassay methods. 

High performance liquid chromatography (HPLC) has been by far the most important method for separating chlorophylls. Open column chromatography and thin layer chromatography are still used for clean-up procedures to isolate and separate carotenoids and other lipids from chlorophylls and for preparative applications, but both are losing importance for analytical purposes due to their low resolution and have been replaced by more effective techniques like solid phase, supercritical fluid extraction and counter current chromatography. The whole analysis should be as brief as possible, since each additional step is a potential source of epimers and allomers. 

Solid phase spectrophotometry proved to be an appropriate technique for the determination of colorants in foods dne to its simplicity, selectivity, reasonable cost, low detection limits, and use of conventional instrnmentation. This simple, sensitive, and inexpensive method allowed simnltaneons determinations of Snnset Yellow FCF (SY), Quinoline Yellow, and their nnsnlfonated derivatives [Sndan I (SUD) and Quinoline Yellow Spirit Soluble (QYSS)] in mixtnres. Mixtnres of food colorants containing Tartrazine, Sunset Yellow, Ponceau 4R, Amaranth, and Brilliant Blue were simultaneously analyzed with Vis spectrophotometry without previous chemical separation. ... 

From the discussion presented of reactions in solids, it should be apparent that it is not practical in most cases to determine the concentration of some species during a kinetic study. In fact, it may be necessary to perform the analysis in a continuous way as the sample reacts with no separation necessary or even possible. Experimental methods that allow measurement of the progress of the reaction, especially as the temperature is increased, are particularly valuable. Two such techniques are thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). These techniques have become widely used to characterize solids, determine thermal stability, study phase changes, and so forth. Because they are so versatile in studies on solids, these techniques will be described briefly. 

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