Spectral techniques

Other methods of sensitive detection of radiotracers have been developed more recently. Eourier transform nmr can be used to detect (nuclear spin 1/2), which has an efficiency of detection - 20% greater than that of H. This technique is useful for ascertaining the position and distribution of tritium in the labeled compound (14). Eield-desorption mass spectrometry (fdms) and other mass spectral techniques can be appHed to detection of nanogram quantities of radiolabeled tracers, and are weU suited for determining the specific activity of these compounds (15). 

Volume 176. Nuclear Magnetic Resonance (Part A Spectral Techniques and Dynamics)... 

Besides the electronic spectral studies noted above, we have also carried out in situ studies of the acidic ruthenium catalyst using nmr and infrared spectral techniques. A key set of observations derive from the and 13C nmr spectra of an operating catalyst at 90° and Pco 1 atm which indicate the presence of only one major ruthenium species. The proton spectrum shows a sharp singlet at 24.0 T which remains such when the solution is cooled to room temperature, although the slow formation of other species was observed over a period of hours at the latter conditions. The 1H-decoupled 13C spectrum of the... 

An electron impact mass spectrum of calcium leuco-vorin has not been obtained because the compound is not sufficiently volatile. It would be difficult to isolate the free acid without first dehydrating the compound. Due to its ionic nature, calcium leucovorin will not dissolve in common silylating reagents. Field desorption, another mass spectral technique, generally lends itself more to compounds like leucovorin. Indeed, this technique has been applied successfully to methotrexate and other folic acid analogs.1 ... 

Photoelectron spectroscopy (PES, a non-mass spectral technique) [87] has proven to be very useful in providing information not only about ionization potentials, but also about the electronic and vibrational structure of atoms and molecules. Energy resolutions reported from PES are in the order of 10-15 meV. The resolution of PES still prevents the observation of rotational transitions, [79] and to overcome these limitations, PES has been further improved. In brief, the principle of zero kinetic energy photoelectron spectroscopy (ZEKE-PES or just ZEKE, also a nonmass spectral technique) [89-91] is based on distinguishing excited ions from ground state ions. 

When one looks at the hydrogens in the chair conformation of cyclohexane, one can see that they are of two types. Six of them are parallel to the central rotational axis of the molecule, so are termed axial. The other six are positioned around the outside of the molecule and are termed equatorial. One might imagine, therefore, that these two t)T>es of hydrogen would have some different characteristics, and be detectable by an appropriate spectral technique. Such a technique is NMR spectroscopy but, at room temperature, only one type of proton is detectable. At room temperature, all hydrogens of cyclohexane can be considered equivalent this is a consequence of conformational mobility, and the interconversion of two chair conformations. 

Equations (if.4) and (ff.S) are solved, along with the continuity equation (which does not change upon nondimensionalization), in a Cartesian coordinate system using the Fourier-Galerkin (spectral) technique under periodic boundary conditions in all three space dimensions. The scheme is similar to that used by Orszag [8] for direct solution of the incompressible Navier-Stokes equations. More details can be found in [9] and [7], and the scheme may be considered to be pseudospectral. ... 

B.A. Borgias and T.L. James, in Methods in Enzymology, Nuclear Magnetic Resonance, Part A Spectral Techniques and Dynamics, Vol. 176, eds N.J. Oppenheimer and T.L. James (Academic Press, San Diego, 1989) p. 169. 

It is of some importance to note that on spectral plates taken using continuous excitation the emissions from the 5Z)1 level are extremely faint. As Bhaumik points out, the time-resolved spectral technique is of great value in energy-transfer studies and is also useful at times in obtaining spectra of short-lived states whose emissions would normally be obscured by other more intense fluorescences. Clearly, it is of value in ascertaining the particular state from which a group of lines originates. 

The adsorption isotherms of Astraphloxin and Pseudocyanine in Figure 8A were also expresed by the Langmuir adsorption equation. The resulting linear relation of Figure 8B demonstrates excellent agreement betwen the data obtained from phase separation and spectral techniques. 

The present article deals with the applications of mass spectrometry to the structural analysis of carbohydrate derivatives. The mass-spectral technique has now become a useful supplement to chemical methods, and provides ready solution of a variety of problems which were a stumbling block in the classical approaches. 

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