Enrichment factor extraction, figure

Alternative 2. By hyphenating an optical fiber sensor for implementing disk-based solid-phase extraction and direct optosensing at the solid surface, there is no need for further elution to perform the optical detection in the eluate phase, as demanded in conventional sorbent-extraction protocols previously reported for sulfide, thus yielding improved enrichment factors [14] (Figure 7.5). 

Body fluids, such as serum, contain several different carotenoids in low amounts. The crucial point in the isolation and analysis of these samples is the enrichment factor. Serum samples can be directly analysed with hyphenated extraction-sample enrichment-separation systems, such as on-line SPE-HPLC employing tailored stationary phases [29]. By using special restricted access materials (RAMs) for sample enrichment, the carotenoids are retarded on the pre-column while the protein binding is broken and the macromolecules are eluted. The preparation of artifacts is hindered, as the whole analysis steps take place under conditions of light- and oxygen-exclusion. The scheme of on-line SPE-HPLC is presented in Figure 5.2.2. 

FIGURE 23-3 Enrichment factor for solute A from solute B as a function of number of extractions for a system in which = V, for various values of Df and Dg as shown. 

Figure 23-3 illustrates that this enrichment factor becomes progressively poorer (larger numerically) as the number of extractions increases. For quantitative recovery of A (a < 0.001) and quantitative separation from B (S b.a 0.001), the distribution ratio for A, Da, must be at least about 10 times larger than Dg. This poor ability for selective separations is the principal disadvantage of the use of batch extractions for recovery or concentration of more than one solute. 

One of the main purposes of membrane extraction in sample preparation is to enrich the analyte, i.e., to increase the concentration of the analyte to permit determination of low concentrations. Plotting the concentration of analyte in the acceptor (Ca) either directly as determined by analysis of the acceptor phase or as a concentration enrichment factor Ee (Ca/Cs— where Cs is the initial concentration in the sample) versus time will typically produce a curve which initially raises approximately linearly and asymptotically eventually reaches a steady equilibrium value. See Figure 12.4 [46]. 

FIGURE 13.5 Enrichment factors for various aniline compounds with different p/sr -values and pH = 0 (ud = 1). (From Chimuka, L., Megersa, N., Norberg, J., Mathiasson, L., and Jonsson, J.A., Incomplete trapping in supported liquid membrane extraction with a stagnant acceptor for weak bases. Anal. Chem., 70, 3906. Copyright 1998 American Chemical Society.)... 

With a large equilibrium distribution coefficient D (complete trapping) and a large phase ratio, Ee will increase linearly up to large values. In Figure 13.5, which refers to an SLM flow system experiment, D in curve 1 is approximately 40,000 and the enrichment factor is linear at least up to at least 6,000 times. In many cases, especially in flow systems, the extraction is not allowed to go to equilibrium, and an extraction efficiency E is defined as the fraction of the total amount of analyte that is transferred to the acceptor. Thus,... 

Plots of the enrichment factor (EF, the metal ion concentration in the receiving phase divided by the metal ion concentration in the source phase) versus time and the chloride ion concentration in the source phase are shown in parts a and b of Figure 4, respectively. Selective permeation of Pb(II) over Cd(II) was observed (Figure 4a), which is the opposite of the extraction efficiencies for these two heavy metal ion species (Table II). The EF for both heavy metals increased with time and reached values of 4.5 and 0.9 for Pb(II) and Cd(II), respectively, after 26 h. 

Figure 5.13 Discrimination diagram for basalts based upon K.-Ta covariations and using Yb as a normalizing factor (after Pearce, 1982). The diagram shows the Belds of volcanic-arc basalts (VAB), MORB and within-plate basalts (WPB). Volcanic-arc basalts are subdivided into tholeiitic (Thol), calc-alkaline (CA) and shos honitic (Sho) varieties. MORB and within-plate basalts are subdivided into tholeiitic (Thol), transitional (Trans) and alkaline (Aik) varieties. Alkaline volcanic-arc basalts also plot in the alkaline held. The plotting coordinates, shown at the margin of the diagram, are extracted from Pearce (1982 — Figure 6). The solid arrows indicate the direction of mantle depletion (D) mantle enrichment (E) and enrichment via a fluid phase (F).

For many small-scale studies, it is unnecessary to purify a DNA-binding factor to complete homogeneity. Instead, over a hundred-fold enrichment of the factor can be achieved by chromatography of one or several ml of a crude nuclear extract directly on a <1 ml affinity column. Conversely, the flow-through from the column is a specific depletion of the DNA-binding factor from the extract. An example of such an enrichment of heat shock activator protein is shown in Figure 3. 

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