Three-dimensional separation

Other groups have also used EC and CE to perform non-comprehensive multidimensional separations (15, 16). A three-dimensional separation was performed by Stromqvist in 1994, where size exclusion chromatography (SEC), reverse-phase HPLC, and CZE were used in an off-line manner to separate peptides (17). The most useful information gained from all of these non-comprehensive studies was knowledge of the orthogonality and compatibility of EC and CE. 

Moore and Jorgenson eombined the rapid two-dimensional separation aehieved by LC-CZE with SEC to make the first eomprehensive three-dimensional separation involving an eleetrodriven eomponent in 1995. Size exelusion ehromatography separated the analytes over a period of several hours while the reverse phase HPLC-CZE eombination separated eomponents in only 7 min. A sehematie diagram of the three-dimensional SEC-reverse phase HPLC-CZE instrument is shown in Eigure 9.9 (18). A dilution tee was plaeed between the SEC eolumn and the reverse phase HPLC injeetion loop in order to dilute the eluent from the SEC eolumn, sinee it eon-tained more methanol than was optimal for the reverse phase HPLC eolumn. 

Figure 9.10 Three-dimensional representation of the data volume of a tryptic digest of ovalbumin. Series of planar slices through the data volume produce stacks of disks in order to show peaks. Reprinted from Analytical Chemistry, 67, A. W. Moore Jr and J. W. Jorgenson, Comprehensive three-dimensional separation of peptides using size exclusion chromatogra-phy/reversed phase liquid chromatography/optically gated capillary zone electrophoresis, pp. 3456-3463, copyright 1995, with permission from the American Chemical Society.

A. W. Moore, Jr and J. W. Jorgenson, Comprehensive three-dimensional separation of peptides using size exclusion chromatography/reversed phase liquid chromatography/ optically gated capillary zone electrophoresis . Anal. Chem. 67 3456-3463 (1995). 

FIGURE 1.3 Three-dimensional representation of a tryptic digest of ovalbumin. The three-dimensional separation consists of size-exclusion chromatography (first dimension), reversed-phase LC (second dimension), and capillary electrophoresis (third dimension). From Moore and Jorgenson, (1995) with permission of the American Chemical Society. 

The LC/MS/MS method utilizes the principle of three-dimensional separation to achieve excellent selectivity based on chromatographic separation (reversed-phase, size-exclusive, ionic, etc.), the unique mass-to-charge ratio of the analyte s parent ion, and the fragment ion. A sample clean up... 

Commercialisation of robust and fast-scanning mass spectrometers, and in particular of ToF MS, has decisively contributed to the increased use of this technique in combination with GCxGC to yield a powerful separation-plus-detection setup providing three-dimensional separation. 

An interesting three-dimensional separated-local-field/dilute-spin-exchange solid state NMR experiment has been reported where homonuclear spin-exchange cross-peaks provide correlation in the un u>z plane. Resonances are resolved along the u> axis by their heteronuclear dipolar couplings. The experiment was demonstrated experimentally with the heteronuclear and N- N homonuclear dipole-dipole interactions in... 

The conclusion from the broad array of examples presented in this chapter is similar to that of the other chapters on IMS applications IMS, in its variety of forms, offers a viable alternate analytical method to traditional chromatographic methods, especially when cost, speed, and sensitivity are important. When samples are complex, however, as in the case of metabolomics for pharmaceutical analyses, chromatographs and MSs can be easily coupled to IMSs to achieve powerful two- and three-dimensional separations. 

Welthagen, W. Mitschke, S. Muhlberger, F. Zimmermann, R. (2007). One-dimensional and comprehensive two-dimensional gas chromatography coupled to soft photo ionization time-of-flight mass spectrometry A two- and three-dimensional separation approach Journal of Chromatography A., Vol.1150, pp. 54-61, ISSN 0021-9673... 

Three-dimensional Separated Flow Topology Critical Points, Separation Lines and Vortical Structures... 

Figure 12.1. Diagram illustrating the versatility of IM-MS instrumentation. In the most common form of IM-MS, (a) the instrument consists of an ion source, a drift cell, a mass analyzer, and a detector. Additional information can be obtained by expanding on this framework, including (b) VTIM-MS, for the determination of structurally resolved thermodynamic and kinetic infmmation (c) IM-MS/MS, for acquisition of nearly simultaneous precursor and fragment ion spectra (d) LC-IM-MS, far three-dimensional separations of complex samples and (e) IM-IM-MS, for further dimensionality in the structural information obtained.

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