Carr-Purcell-Meiboom-Gill train

Phase considerations intrude even in the simplest experiments of observing an FID or an echo. Accurately adjusting the phases of rf pulses can be very important, particularly in experiments involving trains of pulses such as the Carr-Purcell Meiboom-Gill train or the multiple pulse line narrowing sequences. In other sections we have considered how phase shifts originate and how to cope with them. 

The trick introduced by Meiboom and Gill (14) is to dephase all n pulses in the Carr Purcell train by an angle of 90° with respect to the initial ti/2 pulse. It is easily shown that, without this phase change, imperfections of the 71 pulses are cumulative, whereas with the 90° phase change, a self-compensation occurs for all echoes of even number. The CPMG (Carr-Purcell-Meiboom-Gill) experiment can be handled in two ways ... 

Ti reports on fast dynamics on a timescale of ps-ns, whereas T2 relaxation depends on both fast and slower dynamics (ps-ns and xs-ms). The experimentally measured T2 relaxation times include an exchange contribution that can be measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse train (25, 26) or an effective spin-lock field (27-29). The combination of T2 and Tip measurements allows determination of the contribution of chemical exchange to the relaxation time. Eurthermore, relaxation dispersion experiments have been developed to measure slow time-scale xs-ms dynamic processes (30-35). 

Carr-Purcell-Meiboom-Gill (CPMG) experiment. An experiment wherein the net magnetization is allowed tipped into the xy plane, and subjected to a series (or train) of RF pulses and delays to refocus the net magnetization. Maintaining the net magnetization in the xy plane allows the measurement of the T2 relaxation time. 

According to Wiench et al. (2008), a remarkable enhancement of sensitivity can be achieved in Si solid-state NMR by applying the Carr-Purcell-Meiboom-Gill (CPMG) train of rotor-synchronized Ji pulses during the detection of Si magnetization. They used several one- and two-dimensional (ID and 2D) techniques to demonstrate the capabilities of this approach. Examples include ID Si X CPMAS spectra and 2D Si X HETCOR spectra of mesoporous silicas, zeolites, and minerals,... 

It has been demonstrated by Wiench et al that in the case of Si-Si doublequantum techniques, the well known Carr-Purcell-Meiboom-Gill(CPMG) train of rotor-synchronised n pulses during the detection of silicon magnetization can be exploited to measure homonuclear Vsi-si couplings. 

Site populations in Al2Si205 kyanite and short range order parameters in CaAl2Si20g anorthite have been determined by using Al MQMAS NMR with quadrupolar Carr-Purcell-Meiboom-Gill echo train and FAM-II triple quantum to single quantum conversion pulses (MQ-QCPMG-MAS NMR). " ... 

Figure 7.22 The NMR-MOUSE (a) Schematic. The NMR sensor consists of an u-shaped permanent magnet with a solenoidal rf coil placed in the gap. (b) Photo of the NMR-MOUSE testing a tyre, (c) Example of a train of successive Hahn echoes generated according to Carr, Purcell, Meiboom and Gill (CPMG echo train) for carbon-black filled SBR measured by the NMR-MOUSE. The time constant of the echo-envelope defines T...

Figures 2.13, 9.1, and 9.2 demonstrate the formation of an echo following a tt pulse. Application of additional tt pulses can be used to form a train of echoes. It is clear that the dephasing of magnetizations following an echo is of the same form as the initial dephasing during the FID and that application of a second tt pulse at 3T causes a second echo at 4t, etc. The envelope formed by the echo peaks decays according to the real T2, rather than T2, and Fourier transform of each echo provides a set of partially relaxed spectra, from which T2 of each line may be determined. (Carr and Purcell first recognized the value of such a long sequence of TT pulses,104 and their names are usually used to depict the method, but the technique that we described for the spin echo in Chapter 2 and that discussed here include a refinement by Meiboom and Gill,105 as discussed later.)...

The CPMG pulse sequence was first proposed by Carr and Purcell (1954) and modified by Meiboom and Gill (1958). It is composed of a P90 pulse and a train of Pjgo pulses as P tP/go 2TP,go 2TP7go 2x, etc. (Figure 7.16). The T value is, by NMR convention, the time between the middle of the initial P90 and the middle of the next pulse of the sequence, as in Figure 7.16. ... 

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