Separation general characteristics

Chromatography Chromatography is a sorptive separation technique that allows multicomponent separations in both gas and Hquid phase. As a preparative tool, it is often used as a displacement-purge process, although many applications employ an inert-displacement mode, especially for use in analysis. General characteristics and operating modes are discussed in a separate part of this section. 

Proper selection of the filter media is often the most important consideration for assuring efficient suspension separation. A good filter medium should have the following general characteristics ... 

For the SECMIT mode the tip current response is governed primarily by K, Kg, y, and the dimensionless tip-substrate distance, L. Here, we briefly examine the effects of these parameters on the chronoamperometric and steady-state SECMIT characteristics. All chronoamperometric data are presented as normalized current ratio versus in order to emphasize the short-time characteristics, for the reasons outlined previously [12,14-16]. Steady-state characteristics, derived from the chronoamperometric data in the long-time limit, are considered over the full range of tip-substrate separations generally encountered in SECM. 

Table 7.40 summarises the general characteristics of on-line SFC-MS. The method is potentially most useful for thermally labile and involatile compounds that are unsuitable for GC-MS. Because the MS instrument is the main source of information, the reproducibility of the retention and the separation selectivity are much less important than for other SFC applications. As a result, mass spectroscopists do not feel restrained by the limits on reproducibility, which slowed the uptake of SFC by chromatographers. Method development should not be underestimated. Practical problems are associated with interfacing and the effect of the expanding... 

What general characteristic must a component have to be separated by electrophoresis ... 

In choosing suitable methods to separate a given mixture of compounds, the general characteristics favouring a chromatographic method are ... 

Fig. 1 also may be used to note some general characteristics of C spectra of carbohydrate polymers ( -11) Chemical shifts of anomeric carbons (C-l), in the region of 100-110 p.p.m., are typically well separated from other signals. As compared with C-l of the related monosaccharides (12-15)j the anomeric carbon is strongly deshielded (commonly by 7-10 p.p.m.) through glycoside formation (9)> i.e., by the change from 0-H to an 0-C bond. 

General Characteristics of Reversed-Phase Chromatography Separations of... 

The Effect of Alkyl Chain Length on Adsorption. Figure 2 shows that the adsorption isotherms all have somewhat the same general characteristics only the concentrations at which the effects occur appear to depend on the alkyl chain length. Consequently, the adsorption behavior in each of the three regions of the isotherms will be discussed separately and will be interpreted in terms of the role that the hydrocarbon chain plays in the adsorption process. 

For a variety of reasons, it is often necessary to define a feedstock in terms of its physical composition (ASTM, 1995). Furthermore, the physical composition of heavy oils and residua vary markedly with the method of isolation or separation, thereby leading to further complications in the choice of suitable processing schemes for these feedstocks (Speight, 1999 and references cited therein). However, in the simplest sense, petroleum and heavy feedstocks can be considered to be composites of four major fractions (Figure 3-8). The nomenclature of these fractions lies within the historical development of petroleum science and that the fraction names are operational and are related more to the general characteristics than to the identification of specific compound types. Nevertheless,... 

The following table provides a summary of the general characteristics of the most popular stationary phases used in modem high-performance liquid chromatography.1 7 The most commonly used phases are the bonded reverse phase materials, in which separation control is a function of the mobile (liquid) phase. The selection of a particular phase and solvent system is an empirical procedure involving survey analyses. The references provided below will assist the reader in this procedure. 

Figures 8a and b exhibit the time-evolution of scattering curves obtained during a T (temperature)-jump from room temperature to 44°C. The scattering maximum first appears around q=3.1 /tm i and remains stationary for some period, then shifts rapidly to low scattering wave numbers, indicating the nonlinear nature of phase separation in the 10 wt7. HPC solution. The early period of phase separation, at which the peak is virtually invariant, is less obvious at higher T-jumps. Hence, it does not represent the general characteristics of phase separation. In the reverse quench case from 45 to 43°C in Figure 9, the scattering maximum decays with elapsed time without any movement of its position.

The preparation and fabrication methods and their conditions described in Chapter 3 dictate the general characteristics of the membranes produced which, in turn, affect their performance as separators or reactors. Physical, chemical and surface properties of inorganic membranes will be described in detail without going into discussions on specific applications which will be treated in later chapters. Therefore, much of this chapter is devoted to characterization techniques and the general characteristics data that they generate. 

The general characteristics of inorganic membranes that are not application specific but affect separation performance and their determination methods are reviewed in this chapter. Those application-specific characteristics will be treated in Chapters 6 through 11. 

The above example illustrates the general characteristics of a galvanic cell It usually consists of two ionic (or, frequently, solid) solutions in separate but interconnected compartments, in physical contact with electrodes connected to a potentiometer frequently, the electrodes are surrounded by reactive gases. Any departures from the quiescent conditions of open-circuit conditions are accompanied by oxidation-reduction processes that keep in step with the flow of electrons through the external eircuit. 

The discussion on the general characteristics of polymeric and inorganic membranes is treated separately partly due to their differences in production methods and also due to important differences in their operating characteristics. 

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