Offset-saturation experiment

Bain A D and Duns G J 1994 Simultaneous determination of spin-lattioe (T1) and spin-spin (T2) relaxation times in NMR a robust and faoile method for measuring T2. Optimization and data analysis of the offset-saturation experiment J. Magn. Reson. A 109 56-64... 

Measurements of fast exchange rates by the offset-saturation experiment... 

Fig. 9. Pulse sequence for the offset-saturation experiment for measuring T and Tz simultaneously.

Fig. 10. Plot of partially saturated 2 magnetization as a function of irradiation offset in the offset-saturation experiment. The crosses represent experimental values and the line is the...

In this equation, Au i 2 is the chemical shift separation between the exchanging sites, such as the protons in axial and equatorial sites in cyclohexane, and is the exchange contribution to the observed T2, T in eq. (22), which is the T2 determined from the offset-saturation experiment. The ex-... 

A plot of the 2 magnetization (M /Moo) as a function of the irradiation resonance offset is given for an offset saturation experiment on a sample of degassed cyclohexane (CeHn) in CDCI3 at a temperature of 303 K. At this temperature, the cyclohexane resonance was noticeably narrow at 280 K, the linewidth of the cyclohexane resonance was approximately 1.2 Hz, compared to a width of 0.5 Hz for the internal TMS standard. From the resulting values of T and T2, and the measured low-temperature axial-equatorial chemical shift difference of 45.4 Hz at 100 MHz used in eq. (22), the rate at 293 K was determined to be 1.94 x 10 s Thus, rates on the order of 10 or 10 s are accessible in relatively simple systems using the offset-saturation method. 

A plot of the 2 magnetization (Mz/Moo) as a function of the irradiation resonance offset is given in fig. 10 for an offset saturation experiment performed on the aldehydic proton of furfural for a degassed sample of furfural in acetone-de at a temperature of 262.5 0.5 K. 

In fast exchange, we must measure Tz for the coalesced line, and then calculate the exchange rates from that. Standard CPMG and Tip methods may be difficult to implement, but the offset-saturation experiment can be done on essentially any spectrometer. These Tz measurements can often extend the high-temperature side of the Eyring plot by substantial amounts, particularly in the case of unequally populated systems. Taken together with the other methods, they provide excellent data. 

Figure B2.4.6. Results of an offset-saturation experiment for measuring the spin-spin relaxation time, T2- In this experiment, the signal is irradiated at some offset from resonance until a steady state is achieved. The partially saturated z magnetization is then measured with a 7t/2 pulse. This figure shows a plot of the z magnetization as a function of the offset of the saturating field from resonance. Circles represent measured data the line is a non-linear least-squares fit. The signal is normal when the saturation is far away, and dips to a minimum on resonance. The width of this dip gives T, independent of magnetic field inhomogeneity.

Pulse schemes similar to that of the offset-saturation method, often with a homospoil gradient pulse to destroy any x-y magnetization, have been utilized in off-resonance Tip experiments to study intermediate molecular motions in biological systems [107-111] and inorganic compounds [112] from... 

Magnetization transfer (MT) or cross-relaxation spectroscopy, also termed Z-spectroscopy by Grad and Bryant (1990), has been extensively used to obtain information on the spectral Uneshape of protons in macromolecules as well as on relaxation in heterogeneous systems (Calucd and Forte 2009). A MT spectrum was obtained by performing saturation transfer (ST) experiments at many discrete frequencies and plotting the ratio of the steady-state water signal with and without RF saturation as a function of the saturation frequency offset. For spatially homogeneous samples,... 

Experiment LP-02-6 simulated a double-ended offset shear of a commercial PWR main coolant inlet pipe . The principal boundary conditions were (a) coincident loss of offsite power, (b) PWR nominal primary pump coastdown, (c) initial core power representative of USNRC licensing limits in a commercial PWR, and (d) US minimum emergency core coolant (ECC) injection. The cladding thermocouple temperature response was similar to that in LOFT L2-3 as shown in Figure 7. The early return to saturation conditions occurred at the same time, as had been expected. 

Fig.13.18. Schematic diagram of apparatus used by Barger and Hall (1969) for saturated absorption experiments in methane employing the frequency-offset locking technique. (After Hall (1973).)...

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