Pulsed NMR method

Although it s possible to acquire many spectra in rapid succession using pulsed NMR methods, one needs to be aware that the speed with which multiple FIDs can be acquired is still subject to the fact that the nuclei in the sample need to relax between acquisitions (Section 5.1). If successive FIDs are acquired too rapidly, intensity information will be distorted because those nuclei which relax slowly will not be fully relaxed when subsequent scans are acquired and they will contribute less to the resulting signal. To ensure that the signal intensities are accurate, the repetition rate needs to be such that even any slowly relaxing nuclei in the sample are fully relaxed between scans. 

How can T2 and T1 be measured T2 for fluids can often be estimated from the width of the band Av at half-height (Eq. 3-53). However, pulsed NMR methods are usually employed, the measurement of T] being especially easy. 

The ultrafast infrared vibrational echo experiment and vibrational echo spectroscopy are powerful new techniques for the study of molecules and vibrational dynamics in condensed matter systems. In 1950, the advent of the NMR spin echo (1) was the first step on a road that has led to the incredibly diverse applications of NMR in many fields of science and medicine. Although vibrational spectroscopy has existed far longer than NMR, the experiments described here are the first ultrafast IR vibrational analogs of pulsed NMR methods. In the future, it is anticipated that the vibrational echo will be extended to an increasingly diverse range of problems and that the technique will be expanded to new pulse sequences, including multidimensional coherent vibrational spectroscopies such as the vibrational echo spectroscopy technique describe above. 

If you go to a social gathering and announce that you are an expert in relaxation, you could receive responses ranging from curious stares to hearty approvals neither of which are probably justified. In this chapter, we discuss nuclear spin relaxation, a subclass of the larger subject, in a qualitative way as well as pulse NMR methods for measuring them. 

N. Boden, "Pulsed NMR methods," in Determination of Organic Structures by Physical Methods, edited by F. C. Nachod and J. J. Zuckerman (Academic Press, New York, 1971), volume 4, chapter 2, pp. 51-137. 

The simplest ID NMR experiments involve the apphcation of a pulse followed by observation of the resulting signal in the time domain, with subsequent Fourier transformation of the data to the frequency domain for presentation in a format that we, as chemists, can understand. Pulsed NMR methods had their inception in 1966 [33] and have almost completely supplanted earlier continuous wave (CW) methods. For reasons of sensitivity, only ID NMR spectra were typically acquired prior to the 1970s. The advent of pulsed Fourier transform NMR instruments made it possible to acquire natural abundance C NMR spectra on a routine basis in the early 1970s. With the routine availabihty of C NMR data came the compilation of chemical shift data bases and a very different way of approaching chemical structure elucidation. 

Kobayashi M, Kanekiyo M, Ando I (1998) A study of molecular motion of PVA/water system by high-pressure H pulse-NMR method. Polym Gels Netw 6 347... 

Pulsed NMR method, which is used to determine binodal compositions based on differences in decay times of nuclear spins from polymer-rich and polymer-lean phases. 

The second technique to eliminate the term is the so-called multiple-pulse NMR method developed by Waugh et al. The term is eliminated by averaging in spin space with the use of a specially devised four-pulse sequence (WA-HU-HA). This technique is generally applicable to NMR of systems with abundant spins, for instance H NMR of organic compounds. However, the multiple-pulse technique is not widely used at present due to difficulties in controlling the... 

The diffusive motion of the fluorine ions in LaFs was studied in greater detail by means of pulsed NMR methods by Goldman and Shen (1966) and in powdered samples containing Pr " and Nd ions by Shen (1968). The measurements of Goldman and Shen (1966) utilized single crystals and covered the... 

Pulse NMR implies that a spectrum is obtained with an excitation pulse followed by detection of a free-induction decay (FID) and subsequent Fourier transformation. Pulse NMR methods are suitable for rapid and real-time measurements, which is the major requirement in manufacturing industries wishing to improve efficiency in quality and process control. The older field swept continuous-wave (CW) NMR technique - no longer used - carried considerable limitations for rapid measurements. 

There are various methods to determine D, including the pulsed NMR method, the tracer method, and chromatography. Readers are referred to a detailed description, including characteristics, of measurement, in Part 2, Chapter 2, Section 4, Transport and Permeability (Material Diffusion). The measurement of D is done in what follows here by pulsed NMR. 

Pulse-NMR method s main advantage is the time gain compared to the extraction methods, the time of analysis is very short (a few minntes) versns a few days. Pulse-NMR instruments are easy to maintain, official methods nsing this technology have been published (AOCS Ak 3-94 ISO 5511 1992 ISO 10632 2000 ISO 10632 2000 AOCS Ak 4-95) making it easy to nse this technology for conunercial analyses. The analysis is usnaUy condncted on whole seeds and reqnires minimum to no sample preparation. PnIse-NMR usually requires few samples (could be as low as five) for calibration as opposed to other spectrophotometric methods snch as NIR which could require up to several thousands for calibration purposes. 

The oilseed section uses a three-tiered system in order to ensure accurate results obtained with the pulse-NMR method. First, the checksamples are analysed with every analysis and the rapid method results are compared with the reference method results. Second, throughout the year, samples are randomly taken, analysed by both methods and the results compared. Finally, verification samples are made annually and analysed using both the methods. The results from the 2011 verification... 

Gradients are useful as an integral part of multiple-pulse NMR methods. High-resolution NMR systems and probes continue to incorporate these devices and accordingly the use of these tools continues to be-... 

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