Elution incomplete

Trimesic acid, on the other hand, appeared to be so strongly adsorbed to the anion-exchange resin that it was incompletely recovered in the eluate. As discussed earlier, glycine also appeared to bind tightly and to elute incompletely by the standard protocol. Both of these compounds probably could be eluted with aqueous eluents of high ionic strength, but this process would create the problem of recovering the solute from the eluate. Volatile buffers may offer a solution to this problem. 

The behavior predicted by this equation is illustrated in Fig. 16-33 with N = 80. Xp = (Evtp/L)/[il — )(p K -i- )] is the dimensionless duration of the feed step and is equal to the amount of solute fed to the column divided by tne sorption capacity. Thus, at Xp = 1, the column has been supplied with an amount of solute equal to the station-aiy phase capacity. The graph shows the transition from a case where complete saturation of the bed occurs before elution Xp= 1) to incomplete saturation as Xp is progressively reduced. The lower cui ves with Xp < 0.4 are seen to be neany Gaussian and centered at a dimensionless time - (1 — Xp/2). Thus, as Xp 0, the response cui ve approaches a Gaussian centered at Ti = 1. 

If the ion exchange column is loaded with several ions of similar charge, B, C, etc., elution curves may be obtained for each ion by the use of appropriate eluants. If the elution curves are sufficiently far apart, as in Fig. 7.2, a quantitative separation is possible only an incomplete separation is obtained if the elution curves overlap. Ideally the curves should approach a Gaussian (normal) distribution (Section 4.9) and excessive departure from this distribution may indicate faulty technique and/or column operating conditions. 

Under circumstances where two solutes are incompletely resolved and one of the pair is present at a much lower concentration than the other, the profile of the pair often resembles a normal peak with slight asymmetry. Consider the combined elution profile of the two peaks shown in figure 3. 

Surface Adsorption Hater sample is passed through a column of the adsorbent and the adsorbed organic constituents subsequently eluted with a smaller volume of organic solvent. All sample types Adsorbents Include charcoal, macroretlcular resins, polyurethane foams, bonded phases and ion-exchangers. Generally have high capacity but sample discrimination may be a -problem. Sample modification and Incomplete recovery are further possible problems. 

The separation of interactions by 2D spectroscopy can be compared with 2D chromatography. In a onedimensional thin layer or paper chromatogram, the separation of the constituents by elution with a given solvent is often incomplete. Elution with a second solvent in a perpendicular direction may then achieve full separation. In NMR spectroscopy, the choice of two solvents is replaced by the choice of two suitable (effective) Hamiltonians for the evolution and detection periods which allow unique characterisation of each line. 

Figure 19.7. Cyclic batch elution chromatography obtaining high product purity and high throughput by using incomplete resolution (overlapping bands) and recycling the mixed fraction (mf) to the feedstock (a) Control of band separation and cut points determines fractional impurities t mij mr and Ami /mr2-<4l)> (b) Chromatogram for separation of pure ds- and trans- 1,3-pentadiene. Components 1, isoprene 2, trans- 1,3-pentadiene 3, cis-l,3-pentadiene 4, cyclo-pentadiene. Component 1 is eluted at almost the same time as component 4 of the...

Larger volumes can be applied in some circumstances. See text. c If elution is incomplete, increase concentration of ethylene glycol. 

Polarimetric detection of enantiomers eluted from liquid chromatographic columns employing chiral stationary phases has been described 57 58 and interesting applications have been report-ed 59-60, for example, the study of enantiomerizations during chromatography and the evaluation of optica] purity despite incomplete chromatographic enantiomer separation. By this deconvolution method, based on Beer s and Biot s expressions, optical purities rather than enantiomeric purities are determined60. 

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