Saturation-recovery method

A stacked set of saturation recovery spectra is given in Fig. 2.29, which shows that the signal intensity approaches an equilibrium value Arjo related to the fully relaxed magnetization M0. The intensity Az as a function of r is the integral of the Bloch equation (1.17 a) between M., = Mz and M0, or in terms of intensities, from Ar at time t to A f at time go  

7j is obtained as the reciprocal slope of a semilogarithmic (A — Az) versus x plot. Fig. 2.29 (b) illustrates an example of a convenient graphical evaluation, also including the lg - In conversion necessary when decadic semilogarithmic paper is used. 

13C-NMR-Spektroskopie, eine Arbeitsanleitung mit Ubungen. Georg Thieme Verlag, Stutt-(f) gart, 1977.) 

13C spin-lattice relaxation times of individual nuclei can also be measured by PFT 13C H experiments using a 90°, r, 90 , r. pulse train and noise modulation of the proton decoupling frequency. This method is known as progressive saturation [43] and is based on the following concept. 

According to eq. (2.27), 7) is obtained as the reciprocal slope of the semilogarithmic plot of (As — Aj versus x (Fig. 2.30(c)). The equilibrium intensity A ix, corresponding to the relaxed magnetization M0 is approximated by recording a PFT spectrum arising from 

---

Whereas in the case of monomer siloxanes, Tj values may be measured by the inversion recovery method [1], we recommend the saturation recovery method for polymer siloxanes due to the very long measuring times. 

Collision of nitroxides with fast-relaxing radicals, such as oxygen and metal ion complexes, causes spin exchange that effectively shortens the spin-lattice relaxation time T of the nitroxide (Hyde and Subczynski, 1989). This effect can be measured either by continuous wave (CW) power saturation techniques or by saturation recovery methods. Collision frequency is directly proportional to the accessibility of the paramagnetic reagent to the nitroxide radical and is defined as... 

Analysis of the response gives the k values, as in the previous method. In this case, however, the preexponential factors are proportional to the Q values rather than the k values. The magnetic saturation recovery method has a distinct advantage over the pulse transient method in the frequently encountered case where one of the If values is very much smaller than the other. Very often, however, the Q values are more nearly comparable, and two exponentials can be detected in the saturation recovery method, even if both cannot be seen in the pulse (rapid-passage) transient method. 

Among the proton relaxation times obtained by the saturation recovery method, the decrease of the H-6 proton relaxation time from... 

Spin-lattice relaxation times (Tx) were obtained by the saturation-recovery method. Transverse relaxation times (T2) for the narrow central component of the line shapes were measured directly from the Lorentzian line shapes. The line shapes are Fourier transforms (FT) of quadrupole echo (QE) or free induction decay (FID) transients. Complete line shapes and long Tx measurements were obtained with a composite pulse QE sequence with a 3.5 psec tt/2 pulse length. Long Tx and weak signal strength made data accumulation tedious A single Tx measurement or spectral line shape often required over 12 hours of data acquisition. 

Deuteron Magnetic Resonance (DMR) measurements at 30.7 MHz have been performed on an a-Zr2PdD2.9 sample between 19 and 460 K. A Bruker CXP 200 spectrometer and a cryogenic probe were used to examine Fourier transform line shapes and relaxation rates. Spin-lattice relaxation rates (Fj Tf ) were obtained by the saturation-recovery method. Transverse relaxation rates (F2=T2 ) were measured from line shapes which were Gaussian in the rigid lattice and Lorentzian when well narrowed. A quadrupole echo sequence was used to measure F and F2 for temperatures less than 345 K. 

Other methods used for determining 7 include the saturation recovery method and the progressive saturation method. Their discussion is beyond the scope of this text. 

Here x from Equation 10.4 is changed to the two-membrane domain FOT and SLOT with the depth fixed (the same spin label is distributed between the FOT and SLOT domains). W(FOT) and W(SLOT) are oxygen transport parameters in each domain and represent the collision rate in samples equilibrated with air. Figure 10.9 illustrates the basis of the discrimination by oxygen transport (DOT) method, showing saturation-recovery EPR signals for 5-SASL in membranes... 

Subczynski, W. K., J. Widomska, A. Wisniewska, and A. Kusumi. 2007a. Saturation-recovery electron paramagnetic resonance discrimination by oxygen transport (DOT) method for characterizing membrane domains. In Methods in Molecular Biology Lipid Rafts, ed. T. J. McIntosh, Vol. 398, pp. 145-159, Totowa, NJ Humana Press. 

A number of pulse-sequence methods are available for measurement of Ti values, and those most commonly used are the methods of saturation recovery (s.r.F.t.),69,70 progressive saturation (p.s.F.t.),71 inversion recovery (i.r.F.t.),72 and the Freeman-Hill modification of in-... 

Thus, in spite of the high estimations of the reserves of bitumen, the two conditions of vital concern for the economic development of tar-sand deposits are the concentration of the resource, or the percent bitumen saturation, and its accessibility, usually measured by the overburden thickness. Recovery methods are based either on mining combined with some further processing or operation... 

Equilibrium acidities are usually determined by titration, either with indicators of known plCa [24] or by following the extent of dissociation spectroscopically (e.g. by UV-spectroscopy [35]). Kinetic acidities, i.e. the rates of deprotonation of acids, can be determined by measuring rates of racemization[36] or rates of H-D or H-T exchange [37, 38], by chemical relaxation experiments (e.g. T-jump method [35, 39]), or by H NMR (line broadening and saturation recovery [40]). 

There are several ways of determining T, the most reliable method probably being saturation-recovery, in which two 90° pulses are applied separated by a time x of the order of Ti. The signal height is then proportional to Mz(x), given by... 

Measurements of longitudinal relaxation would be preferred over measurements of transverse relaxation, because signal attenuation from molecular diffusion in local field gradients near pore walls can then be neglected, but saturation and inversion recovery methods are more time consuming than CPMG experiments, so that transverse relaxation... 

---