Two-dimensional spectrum

However, it is possible to use two-dimensional spectra in spectrophotometry as an alternative. In this case, the pH value of the water phase in extracting systems is used as a supplementary coordinate. 

The system of anionic surfactants is another example of organic compounds mixtures. The procedure of their determination is proposed using coordinate pH in two-dimensional spectra of ionic associates anionic surfactants with rhodamine 6G. This procedure was tested on the analysis of surfactant waters and domestic detergents. 

Two-dimensional spectra are often recorded in the absolute-value mode. The absolute value A is the square root of the sum of the squares of the real (R) and imaginary (/) coefficients ... 

Figure 3.12 Two-dimensional NMR plots recorded at different contour levels, (a) Two-dimensional spectra recorded at low contour level usually have noise lines across the plot, (b) With a higher contour level, many of the noise peaks are eliminated and the peaks become clearer.

K. Nakanishi (ed.), One-Dimensional and Two-Dimensional Spectra by Modem Pulse Techniques, Kodansha, Tokyo (1990). 

Ernst published a method for the identification of cross-peaks in two-dimensional spectra based on the recognition of their unique anti-phase portion in phase-resolved two-dimensional spectra. Glaser and Kalbitzer presented a generalized and fully automated method for the recognition of cross-peaks in two-dimensional NMR spectra. 

Bodenhausen ° developed a pattern-recognition programme (MARCO POLO) in order to extract coupling pathways in COSY spectra. He subsequently described a recursive deconvolution technique for the measurement of couplings, but this seems to offer more benefits to the measurement of scalar couplings in two-dimensional spectra than in one-dimensional spectra. 

Wiithrich et al published a tour de force on the Automated Peak-Picking and Peak Integration in Macromolecular Spectra (AUTOPSY). This work deals primarily with two-dimensional spectra, but the algorithms are equally... 

Whilst scalar couplings are readily identified in two-dimensional spectra, their measurement from cross-peak multiplets poses special problems. 

The confirmation of structure is essentially the same as that described in the previous section, but because of the systematic way in which the well contents are derived, other less demanding analysis tools may be appropriate. One approach is to utilize the spectra of the individual sub-structures. In Bruker s AutoDROP (Automated Definition and Recognition Of spectral Patterns, contained within the AMIX suite of software ) these can derive from spectra (most commonly HSQC two-dimensional spectra) of the reactants or from a basis set of product spectra containing sufficient combinations. The process by which the spectra of the sub-structures are... 

Two-dimensional spectra have the appearance of surfaces, generally with two axes corresponding to chemical shift and the third (vertical) axis corresponding to signal intensity. 

It is usually more useful to plot two-dimensional spectra viewed directly from above (a contour plot of the surface) in order to make measurements and assignments. 

Another way of avoiding overlaps seen in two-dimensional spectra is to introduce the third dimension. This has been illustrated with the 3D NOESY-HOHAHA [21-25], 3D HOHAHA-NOESY [25-27], NOESY-COSY [28, 29], COSY-NOESY [28] and ROESY-TOCSY [23] experiments. A principal drawback, associated with homonuclear 3D techniques, is the low digital resolution achievable along the first and second spectral axes. This limitation can to certain extent be removed by implementing band selective pulses into the 3D homonuclear experiments [21, 26, 28-31]. 

Two-dimensional spectra usually require hours or days of acquisition because separate FIDs are collected... 

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