Recycle delay

FIR) [25], where the recycle delay is made shorter than 5T and the experiment is carried out under the steady-state rather than equilibrium conditions. A still more time-saving variety, the super-fast inversion recovery (SUFIR) has also been proposed [26]. 

The interval between the second and third pulse is called the mixing time, during which the spins evolve according to the multiple-spin version of equation B 1.13.2 and equation B 1.13.3 and the NOE builds up. The final pulse converts the longitudinal magnetizations, present at the end of the mixing time, into detectable transverse components. The detection of the FID is followed by a recycle delay, during which the equilibrium... 

MHz H NMR spectra were measured on solutions of ca 25 mg pectin/0.5 ml D2O on a Bruker AMX600 NMR spectrometer. The temperature was 350 K to diminish the viscosity of these solutions and 32 scans were measured. Solvent suppression was performed using presaturation during the recycle delay. 

Fig. 5.3.9 Hp-129Xe 2D EXSY NMR spectra frequency discrimination (states) with 64 scans recorded during combustion for various ex- per spectrum. The average experimental time change times. Adapted from Ref. [2], The per EXSY with 0.5-s recycle delay was 40—50...

The ZSM-4 sample was prepared following the previously described procedures.[20] The elemental analysis showed that the Si/Al ratio was 3.0. 29Si MAS NMR spectra were recorded at 11.7 T MHz on a Varian InfinityPlus 500 spectrometer on a sample loaded in a 7.5 mm MAS rotor spinning at 4 kHz using a rc/2 rad pulse length and a recycle delay of 360 s. The 29Si chemical shifts are referenced with respect to an external solution of TMS (5Si = 0.0 ppm). 

In the following, we will discuss heteronuclear polarization-transfer techniques in four different contexts. They can be used as a polarization-transfer method to increase the sensitivity of a nucleus and to shorten the recycle delay of an experiment as it is widely used in 1H-13C or 1H-15N cross polarization. Heteronuclear polarization-transfer methods can also be used as the correlation mechanism in a multi-dimensional NMR experiment where, for example, the chemical shifts of two different spins are correlated. The third application is in measuring dipolar coupling constants in order to obtain distance information between selected nuclei as is often done in the REDOR experiment. Finally, heteronuclear polarization transfer also plays a role in measuring dihedral angles by generating heteronuclear double-quantum coherences. 

Samples of about 50 mg are weighed and dissolved in 0.5 mL of (methyl sulfoxide)-d6 (DMSO-d6) and 10 pL of dichloromethane is added. A small portion of this solution is then withdrawn and diluted in an NMR tube with DMSO-d6- 1H NMR integration parameters are as follows 32K data points, recycle delay of 5 s, 30° pulse angle. Measurement is against the hydroxyl proton doublet (2 H) at 8 4.63. If the hydroxyl doublet is not satisfactorily resolved, additional dilution is performed. 

Standard onedimensional NMR One-dimensional NMR — simple one-pulse experiment, typically with presaturation of solvent during the recycle delay with a weak RF field To quantify small molecules To identify some simple small molecules... 

A little less obvious is the setting of the recycle delay RD (for NP-type sequences) or Tp (for PP-type sequences) which is linked through the factor f in Eqs. (3) and (4) to the estimated relaxation time Ti ax of the slowest-decaying component of sample magnetization at a specific field. One cannot influence the sample relaxation times, of course. On the other hand, the relaxation times usually dominate the overall duration of a single... 

The NMR spectra of adsorbed xenon were obtained on a Bruker MSL-300 spectrometer operating at 83.0 MHZ and 295K. Typically, 2000-40000 signal acquisitions were accumulated for each spectrum with a recycle delay of 0.3s between 90 pulses. The Xe NMR chemical shifts were referenced to that of external xenon gas extrapolated to zero pressure using Jameson s equation [11]. All resonance signals of xenon adsorbed in zeolites were shifted downfield from the reference but were taken to be positive in this report. 

To perform a quantitative imaging or spectroscopy experiment, the relaxation time characteristics of all species (and relevant physical states of those species) must be fully characterized so that the pulse angles and delays between pulses are optimized for that particular system. In particular, if successive repetitions of a pulse sequence are applied at time scales ( recycle delays ) of the order of or... 

Prepare the spin echo application with appropriate acquisition parameters. Typically, 90° to 180° pulse separation 3.5 msec, moisture plus oil sample window 0.05 to 0.06 msec, oil sample window 7 msec, number of scans 16, recycle delay 2 sec, detection mode magnitude , and phase cycling (if available) ON . 

Standard correlation spectroscopy (COSY) experiments were run on the same four samples and the results are displayed in Figure 8.2.16. Since the acquisition time was approximately an order of magnitude less than the recycle delay, a full factor of four for improvement in throughput was achieved in fact, the number of coils could be increased for yet further improvements in temporal efficiency. No signal bleedthrough was observed from one spectrum to another. Similar results were reported in this paper with a two-coil probe used at 500 MHz [19]. 

Figure 8.2.16 COSY spectra acquired with the four-coil probe, where the compounds and concentrations were the same as those of the one-dimensional spectra. Data acquisition parameters spectral width, 2000 Hz data matrix, 512 x 128 (complex) 16 signal averages delay between successive coil excitations, 400 ms effective recycle delay for each sample, ca. 1.7 s. Data were processed by using shifted sine-bell multiplication in both dimensions and displayed in magnitude mode. Reprinted with permission from Li, Y., Walters, A., Malaway, P., Sweedlar, J. V. and Webb, A. G., Anal. Chem., 71, 4815M820 (1999). Copyright (1999) American Chemical Society...

ID 13C NMR N/A Can provide a quantitative overview as to the carbon distribution. In the case of NOM, often 2D NMR is central to the interpretation of the ID NMR, which often contains considerable overlap. For quantitative data, the recycle delay (dl) should be >5 x T1 for the slowest relaxing component in the sample and inverse gated decoupling should be carried out, to prevent the transfer of XH NOE to the BC nuclei. 

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