2D chromatogram

The 2D chromatograms reveal additional components of the natural mixtures. They also give a map of the essential oil, which is helpful in the identification of the components by the position and the characteristic colours of the derivatives on the plate. A further, considerable improvement in the separation performance can be obtained by using overpressured layer chromatography (OPLC). Harmala et al. (70) used 2D OPLC for the separation of coumarins from the genus Angelica. Figure 10.15 shows the one-dimensional (a) and two-dimensional (b) OPLC separations of 16 coumarins. 

Phillips and Xu have presented two-dimensional (2D) chromatograms of kerosines, separated with different stationary phase combinations, in many thousands of components (37). Frysinger et al. have separate benzene-toluene-ethyl benzene-xylenes (BTEX) and total aromatics in gasolines by using GC X GC... 

Equations 4.22 1.24 are the 2D equivalents of Equations 4.17 1.20. The comparison of the two sets of equations shows a surprising consequence. If the peak capacities of the 1D and 2D separation systems were identical, the 2D separation would lead to more severe overlap. In order to have the same number of components isolated as singlets with a 1D and a 2D separation system, the peak capacity of the 2D system ( 2d) should be double of that of the ID system (nw). Ideally, in an orthogonal system 112D = n j D, but part of the gain in peak capacity is lost due to the increased probability of peak overlap provided the 2D chromatogram is disordered. 

A multicomponent 2D chromatogram is considered as a series of 2D peaks with random position and height. For the sake of simplicity, here we assume that the peaks are modeled with bidimensional Gaussian peaks, thus the signal is expressed as... 

The 2D autocovariance function can also be calculated from the 2D chromatogram acquired in digitized form,... 

Most often, real 2D chromatograms exhibit a composite ordered and disordered characteristic, that is, a series of disordered spots are superimposed over ordered spot sequences. When the chromatogram is derived from a mixture of several chemical families, a superficial look at the 2D separation map may give the impression of randomness. In that case, the autocovariance function, however, can resolve and help identify the hidden structured nature of the map. 

FIGURE 8.4 2D chromatogram of a AEX x RPLC separation of reduced porcine thyro-globulin. Reprinted from Holland and Jorgenson (2000), by permission of John Wiley Sons, Ltd. 

FIGURE 8.5 2D chromatogram of a CEX x RPLC separation of an E. coli lysate. Reprinted with permission from Opiteck et al. (1997), copyright 1997, American Chemical Society. 

D chromatograms were prepared by loading total ion current (TIC) data from each reversed-phase chromatogram from MassLynx onto the data analysis software... 

In comparing the three chromatograms, it is apparent that the general shape of the elution profile is the same for all the three runs. Numerous peaks appear within the first 12 min of anion-exchange retention time in all three 2D chromatograms. These correspond to the proteins that were not-retained or very weakly retained on the anion-exchange column, which implies that they are the most basic proteins in the sample. 

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