Two-Dimensional Techniques

One technique for high dimensional data is to reduce the number of dimensions being plotted. For example, one slice of a three-dimensional data set can be plotted with a two-dimensional technique. Another example is plotting the magnitude of vectors rather than the vectors themselves. 

Other two-dimensional techniques, such as COSY (122), DEPT (123), HOHAHA, soHd state (124) etc. give varying degrees of success when apphed to the stmcture-property relationship of cellulose triesters. The recent appHcation of multiple-bond correlation (HMBC) spectroscopy for... 

A number of other, more sophisdcated, selective averaging tools (includli spin echo, double resonance and two-dimensional techniques) are available, both for spectral editing purposes and for obtaining quantitadve information about inter-... 

Two-dimensional gel electrophoresis (2DE) is a two-dimensional technique for protein separation, which combines isoelectric focusing and sodium dodecyl sulphate (SDS) electrophoresis. The high resolving power results from separation according to charge (isoelectric point) in the first dimension and size (mobility in a porous gel) in the second dimension. Depending on the gel size, from several hundred to more than 5,000 proteins can be separated. 

A detailed analysis of the proton high field NMR spectra of tomato juice and pulp has recently been acquired [15]. The combination of suitable selective and two-dimensional techniques (J-resolved, COSY, TOCSY, DOSY, etc.) was used for... 

Thannhauser, T. W., McWherter, C. A., and Scheraga, H. A., Peptide mapping of bovine pancreatic ribonuclease A by reverse-phase high-performance liquid chromatography. II. A two-dimensional technique for determination of disulfide pairings using a continuous-flow disulfide detection system, Anal. Biochem., 149, 322, 1985. 

Other reviews of multidimensional separations have been published. These include a book on polymer characterization by hyphenated and multidimensional techniques (Provder et al., 1995), a review on polymer analysis by 2DLC (van der Horst and Schoenmakers, 2003), and two reviews on two-dimensional techniques in peptide and protein separations (Issaq et al., 2005 Stroink et al., 2005). Reviews on multidimensional separations in biomedical and pharmaceutical analysis (Dixon et al. 2006) and multidimensional column selectivity (Jandera, 2006) were recently published. Suggested nomenclature and conventions for comprehensive multidimensional chromatography were published in 2003 (Schoenmakers et al., 2003), and a book chapter in the Advances in Chromatography series on MDLC was published in 2006 (Shalliker and Gray 2006). 

Certainly two-dimensional techniques have far greater peak capacity than onedimensional techniques. However, the two-dimensional techniques don t utilize the separation space as efficiently as one-dimensional techniques do. These theories and simulations utilized circles as the basis function for a two-dimensional zone. This was later relaxed to an elliptical zone shape for a more realistic zone shape (Davis, 2005) with better understanding of the surrounding boundary effects. In addition, Oros and Davis (1992) showed how to use the two-dimensional statistical theory of spot overlap to estimate the number of component zones in a complex two-dimensional chromatogram. 

HMBC //eteronuclear multiple frond correlation. A proton-detected, two-dimensional technique that correlates protons to carbons that are two and three bonds distant. Essentially, it is an HMQC that is tuned to detect smaller couplings of around 10 Hz. 

INADEQUATE Incredible natural abundance double quantum transfer experiment. Two-dimensional technique showing 13C-13C coupling. It should be the holy grail of NMR methods but is in fact of very limited use due to extreme insensitivity. 

J-resolved spectroscopy Two-dimensional techniques, both homo- and heteronuclear, that aims to simplify interpretation by separating chemical shift and coupling into the two dimensions. Unfortunately prone to artifacts in closely coupled systems. 

NOESY Nuclear Overhauser effect spectroscopy. Two-dimensional technique that correlates nuclei to each other if there is any NOE between them. 

TOCSY Total correlation spectroscopy. One and two-dimensional techniques that are analogous to COSY but which differ in that it shows couplings within specific spin systems. 

A variety of computer-controlled pulse sequences consisting of two or more pulses of appropriate length, frequency range, power and phase, and separated by variable time intervals, has been developed, giving rise to families of 1-D (one-dimensional) and 2-D (two-dimensional) techniques. These techniques provide additional or more easily interpreted data on coupled nuclei, facilitating the identification of signals from chemically different groups of nuclei and correlations between spectra from different elements in the same compound. 

A two-dimensional technique involving initial separation by high voltage electrophoresis at pH 2.0 followed by chromatography is a useful means of separating similar amino acids and short peptides and does not require desalting or excessive purification of the sample (Figure 10.17). 

Two-dimensional techniques are usually employed if both phospho-glycerides and glycolipids are present, but it is possible to resolve members of both classes using a diisobutylketone-acetic acid-water mixture (40 25 5). A solvent composed of acetone, acetic acid and water (100 2 1) will separate the mono- and di-galactosyldiglycerides, which are particularly abundant in plant extracts, from phosphoglycerides, which remain at the origin. 

Since the advent of pulsed NMR spectroscopy, a number of advanced two-dimensional techniques have been devised. These methods afford valuable information for the solution of complex structural problems. The technical detail behind multi-dimensional NMR is beyond the scope of this book. 

There are a number of techniques stemming from the basic two-dimensional technique, which for example allow correlation between carbon atoms and the protons attached to them and correlations of carbon atoms with protons one or two bonds removed from them, heteronuclear multiple bond correlation (HMBC). 

Bertsch, W. (1978) Methods in high resolution gas chromatography Two-dimensional techniques. f High Resolut. Chromatogr. Chromatogr. Commun. 1 85-90, 187-194, 289-297. 

GAGs are separated by electrophoresis to yield a distinct pattern for the different MPS types [32, 33]. It was found that electrophoresis in barium acetate depends largely on the structure of the GAGs, whereas the degree of sulfatation is of minor importance [69]. One-dimensional electrophoresis, as described here, offers lower resolution than two-dimensional techniques [28], but is simpler to evaluate and allows the assessment of several patients in one run. 

In the future, we can expect the development of novel experimental techniques in solid-state NMR spectroscopy for investigation of functioning catalysts. Important goals are (i) the enhancement of the sensitivity of solid-state NMR spectroscopy, for example, by a selective enhancement of the nuclear polarization taking advantage of laser-polarized xenon, (ii) increases in the temperature range accessible for the characterization of solid-catalyzed reactions, and (iii) the coupling of NMR spectroscopy with other techniques such as mass spectrometry. Furthermore, modern two-dimensional techniques of solid-state NMR spectroscopy such as MQMAS NMR spectroscopy will be applied to improve the resolution of the spectra. 

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