Multidimensional separation, techniques

Reinders, J., Zahedi, R.P., Pfanner, N., Meisinger, C. and Sickmann, A. (2006a) To ward the Complete Yeast Mitochondrial Proteome Multidimensional Separation Techniques for Mitochondrial Proteomics. J. Proteome Res. 5,1543-1554. 

Zhao, Y Chow, D.T. Thomas, S. Yin, L. Semin, D. Rapid Analytical Method Development in Support of Medicinal Chemistry Using Parallel and Multidimensional Separation Techniques, in Proceedings of the HPLC2003 Symposium, Nice, France, June 15-19, 2003, p. 149. 

A general discussion on dimensionality in analytical chemistry appears in [3]. Physical, chemical, measuring, and statistical dimensionality are considered. Multidimensional separation techniques are defined [4] as being the result of two or more independent separation steps that are linked together. 

Important applications of Af-PLS are in the area of multivariate calibrations for excitation/emission fluorescence spectrometry, for hyphenated analytical methods, such as HPLC/diode array detection and GC/MS, or for multidimensional separation techniques with or without coupling to spectroscopy. 

The multidimensional distributions in hb polymers - that is, molar mass and DB-require the use of multidimensional separation techniques. For example, two-dimensional liquid chromatc raphy (2D-LC) [156] can provide simultaneous information on both molar mass and structural characteristics such as topol<, by combining SEC and interaction chromatography into one measurement. These investigations were conducted intensively for the separation of stars or long-chain branched polymers from linear analogs [157-160], and demonstrated the great potential of 2D-LC separations. Until now, the apphcation of 2D-LC has been... 

In the 50 years since its introduction, the use of GC by the petroleum industry has helped foster many breakthroughs in GC instrumentation. Open-tubular GC columns and the theory that describes them were first introduced by Golay and Ettre in the mid-1950s. The further development of open-tubular capillary columns was done by Desty of British Petroleum, and, with subsequent refinement, this technique is now the standard method for most GC applications. The use of GC for sample analysis was also quickly adopted by the pharmaceutical and food industries and is used for fundamental studies of reaction kinetics and physiochemical measurements. Today the use of GC for the analysis of complex samples such as serum proteins, natural products, essential oils, and environmental samples has become a routine with multidimensional separation techniques and multivariate chemometric analysis providing identificatimi and quantification of trace analytes from complex samples in the sub-ppb range. A GC system usually consists of the following elements (Fig. 1) ... 

MS can be combined with traditional multidimensional separation techniques that significantly improve the selectivity and specificity of the experimental approach for use in increasingly complex polymer applications. 

Multidimensional separation techniques have been developed with a number of objectives such as increased perik capacity and/or Improved resolution for the separation of highly complex samples, shortened analysis time via heartcut and partial analysis of fractions from complex samples, and enhanced detection of trace components. Both GC-GC, LC-GC, and LC-LC methods as well as various other multidimensional combinations involving CZE or SEC have been described and coupled to mass spectrometry. In most cases, the multidimensional approach comprises a combination of two chromatographic columns, either containing two different stationary phases (both GC and LC), or developed with two different mobile phases (LC only). The sample is injected onto the first column. Part of the chromatogram is heart-... 

The on-line combination of LC-LC-MS has been investigated for a number of reasons. In addition to the general prospects of multidimensional separation techniques, especially enhanced selectivity, there was special interest in the ability to perform LC-LC with two different mobile-phase compositions. In this way, it should be possible to avoid problems with mobile-phase incompatibility due to the use of nonvolatile mobile-phase constituents. A good example of this approach is the determination of enantiomers of p-blockers in plasma samples, described by Edholm and co-workers. Racemic mixtures of a p-blocker like metoprolol can be separated on a ai-acid glycoprotein column. However, the chromatography requires the use of a 20 mM phosphate buffer (pH 7) in the mobile phase, which is not compatible with on-line LC-MS. Therefore, the chiral column was coupled via a set of two trapping columns to a common reversed-phase LC column. After separation, the two enantiomers were sepa-... 

Multidimensional or hyphenated instmments employ two or more analytical instmmental techniques, either sequentially, or in parallel. Hence, one can have multidimensional separations, eg, hplc/gc, identifications, ms/ms, or separations/identifications, such as gc/ms (see CHROMATOGRAPHY Mass spectrometry). The purpose of interfacing two or more analytical instmments is to increase the analytical information while reducing data acquisition time. For example, in tandem-mass spectrometry (ms/ms) (17,18), the first mass spectrometer appHes soft ionization to separate the mixture of choice into molecular ions the second mass spectrometer obtains the mass spectmm of each ion. 

J. C. Giddings, Use of multiple dimensions in analytical separations in Multidimensional Chromatography Techniques and Applications, H. J. Cortes (Ed.), Marcell Dekker, New York, Ch. 1-27 (1990). 

Another means of realizing multidimensional separation is combination of two complementary separation techniques which use different methods of separation. In such multi-modal separation, different techniques can be coupled in which PC is used as the second dimension and another separation method, as the first. Some possible variations are as follows ... 

This chapter will first cover the nature of electrophoretic separations, especially those concerning capillary electrophoresis. Comprehensive multidimensional separations will then be defined, specifically in terms of orthogonality and resolution. The history of planar and non-comprehensive electrodriven separations will then be discussed. True comprehensive multidimensional separations involving chromatography and capillary electrophoresis will be described next. Finally, the future directions of these multidimensional techniques will be outlined. 

Electrodriven separation techniques are destined to be included in many future multidimensional systems, as CE is increasingly accepted in the analytical laboratory. The combination of LC and CE should become easier as vendors work towards providing enhanced microscale pumps, injectors, and detectors (18). Detection is often a problem in capillary techniques due to the short path length that is inherent in the capillary. The work by Jorgenson s group mainly involved fluorescence detection to overcome this limit in the sensitivity of detection, although UV-VIS would be less restrictive in the types of analytes detected. Increasingly sensitive detectors of many types will make the use of all kinds of capillary electrophoretic techniques more popular. 

Electrodriven techniques are useful as components in multidimensional separation systems due to their unique mechanisms of separation, high efficiency and speed. The work carried out by Jorgenson and co-workers has demonstrated the high efficiencies and peak capacities that are possible with comprehensive multidimensional electrodriven separations. The speed and efficiency of CZE makes it possibly the best technique to use for the final dimension in a liquid phase multidimensional separation. It can be envisaged that multidimensional electrodriven techniques will eventually be applied to the analysis of complex mixtures of all types. The peak capacities that can result from these techniques make them extraordinarily powerful tools. When the limitations of one-dimensional separations are finally realized, and the simplicity of multidimensional methods is enhanced, the use of multidimensional electrodriven separations may become more widespread. 

Chromatography is the best technique for the separation of complex mixtures. Frequently, samples to be analysed are very complex, so the analyst has to choose more and more sophisticated techniques. Multidimensional separations, off-line and recently on-line, have been used for the analysis of such complex samples. 

Barth, H. G., Hyphenated polymer separation techniques present and future role, in Chromatographic Characterization of Polymers, Hyphenated and Multidimensional Techniques, Provder, T., Barth, H. G., and Urban, M. W., Eds., American Chemical Society, Washington, D.C., 1995, chap. 1. 

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