Contour plotting identification

AES type surfactants were examined qualitatively in the ESI—FLAMS mode but, from the result, the presence of AES seemed to be doubtful. After a LC separation presenting the TIC in the form of a contour plot the identification of AES surfactants in parallel with an amphoteric surfactant mixture of alkylamido propyl betaine type was possible [50]. 

Fig. 70.3 En ergy level diagram of a two spin J4 system / and S showing the identification of com ponents of the 2D multiplet expressed via single transition basis operators, Z13, I24, S12, S34. Contour plots of a N- H backbone moiety with...

Fig. 2.54 presents a two-dimensional carbon-proton shift correlation of D-lactose after mutarotational equilibration (40% a-, 60% / -D-lactose in deuterium oxide), demonstrating the good resolution of overlapping proton resonances between 3.6 and 4 ppm by means of the larger frequency dispersion of carbon-13 shifts in the second dimension. The assignment known for one nucleus - carbon-13 in this case - can be used to analyze the crowded resonances of the other nucleus. This is the significance of the two-dimensional CH shift correlation, in addition to the identification of CH bonds. For practical evaluation, the contour plot shown in Fig. 2.54(b) proves to be more useful than the stacked representation (Fig. 2.54(a)). In the case of D-lactose, selective proton decoupling between 3.6 and 4 ppm would not afford results of similiar quality. 

For structural identification of the fractions, the XH-NMR spectrometer was directly coupled via capillary tubing to the chromatograph. The injection of the sample into the HPLC system was automatically initiated by the NMR console via a trigger pulse when starting the acquisition of NMR data. Using an appropriate pulse sequence, both solvent resonances (ACN at 2.4 ppm and water at 4.4 ppm) could be suppressed simultaneously. As a result of the on-line HPLC-NMR experiment, a contour plot XH chemical shift vs. retention time was generated (see Fig. 39). Due to the efficient solvent suppression, the obtainable structural information relates to the entire chemical shift region. From the contour... 

Recently, NMR spectrometers directly coupled with LC systems have become commercially available. Spectra can be acquired in either of two modes, continuous or stopped flow. In continuous flow mode the spectrum is acquired as the analyte flows through the cell. This method suffers from low sensitivity since the analyte may be present in the cell for only a brief period of time, but it has the advantage of continuous monitoring of the LC peaks without interruption. Fig. 12A shows a contour plot of the continuous flow NMR analysis of a mixture of vitamin A acetate isomers.Fig. 12B shows the spectra taken from slices through the contour plot. These plots highlight the olefinic region of the spectra which provided ample information for the identification of each of the isomers. With very limited sample quantities, the more common method of LC-NMR analysis is stopped flow. Here the analyte peak is parked in the flow cell so any of the standard NMR experiments can be run. 

Figure 27. While the information content of the two presentations is identical, the stacked plot is related more easily to a conventional spectrum, and therefore used more widely when identification of individual peaks is of primary interest, as in J-spectroscopy. On the other hand, a contour plot is more economical when one is attempting to establish connectivities between atoms by an observation of cross peaks, as in COSY and NOESY spectra. Here a contour projection of the normal spectrum is plotted on the diagonal, and the cross peaks can be identified readily on the projections of their coordinates, as shown in Figure 26. The cross peaks in the COSY spectrum are indicative of spin-spin coupling between the two groups on the diagonal. The cross peaks in the NOESY spectrum indicate the existence of crossrelaxation between the two groups.

Figure 2 Visual identification of analyte degradation in the injector and/or in the D column in the contour plot (right side) and in nonconverted chromatograms (left side) [1]. Peak identification (1) chlorothalonil, (2) vinclozolin, (3) metalaxyl, (4) penconazole, (5) procymidone, (6) myclobutanil, (7A, 7B) propiconazole diastereomers, (8) tebuconazole, (9B) iprodione, and (9A) iprodione degradation product.

FIGURE 6.13 Contour plot of the comprehensive HPLC analyses of carotenoids present in sweet orange essential oil with peaks and compound classes indicated (for peak identification see Ref. 136). (From Dugo, P. et al., 2006. Anal. Chem., 78 7743-7750. With permission.)... 

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