The ge-2D TOCSY experiment allows to obtain a 2D TOCSY spectrum with a single scan per t1 increment provided that the S/N ratio is adequate. The main advantage of such approach is the large reduction in the total acquisition time compared with a conventional 2D TOCSY experiment. The TOCSY experiment permits to correlate all protons resonances belonging to the same spin system via the homonuclear J_HH coupling constants.

Easy implementation on any AVANCE spectrometer equipped with pulsed field gradients.

The gradient-enhanced version of the 2D TOCSY experiment is easily made by incorporating two PFGs, just before and after the mixing process ( 90JMR422-87 ). When these gradients have the same duration and intensity, N-type data is selected in a single scan per t1 increment and, therefore, a magnitud-mode COSY spectrum can be quickly recorded in a few minutes. ( 96JMRA246-123 ). On the other hand, phase-sensitive TOCSY spectra can also been obtained using the echo-antiecho approach (97JMR145) in which  the amplitude of the refocusing gradient is inverted in alternated scans, or using an strong spin-lock or a z-filter pulse prior to acquisition ( 97JMR145-125 ). Recently, it has been shown that sensitivity-improved TOCSY spectra can be easily obtained including the PEP methodology in the echo-antiecho approach ( 98JMR162-130 ). A z-filtered DIPSI scheme is applied as a mixing time and the phase of the 90º pulse preceeding the DIPSI train pulse is also inverted in alternate scans, simultaneous to the refocusing gradient. The use of gradients allows to obtain clean and high-sensitive TOCSY spectra using a minimum two-step phase cycle.

2D TOCSY experiments can include gradient-based  solvent suppression schemes as, for instance, the WATERGATE  ( 92JB661 , 96JMRB168-111 , and 96JB213 ) or DPFGE ( 96JMRB82-112 , and 97JMR93-129 ) schemes optionally combined with a water-flip-back pulse prior to acquisition and the WET scheme during the preparation period ( 95JMRA295-117 ). Modified WATERGATE ( 96JMRB124-110 ) and DPFGE schemes ( 98JB437 ) for multiple-solvent suppression purposes in TOCSY experiments have been also proposed.

Recently, the use of adiabatic TOCSY mixing sequences has been proposed.

This experiment is acquired an processed using the same experimental conditions as described for its phase cycle version. The only difference is the presence of the gradients. Thus, the user only need to define the strength, duration, shape of the gradients and the recovery delay.

The ge-2D TOCSY experiment can be recorded in routine and automation modes using a single scan per increment t1 and minor changes are required if a predefined parameter set is available. The most important parameter to consider is the duration of the mixing time.

More details on practical implementation of ge-2D TOCSY experiments on AVANCE spectrometers can be found in

Tutorials: 2D homonuclear experiments

Tutorials: 2D gradient-based homonuclear experiments

Tutorials: 2D gradient-based homonuclear experiments in H₂O

The magnitude-mode spectrum resulting of the gradient-enhanced TOCSY version is a clean 2D map in which t1 noise has been efficiently reduced. As in the conventional TOCSY spectrum, cross-peaks correlate chemical shifts between J-coupled and relayed spins belongign to the same spin system. Four main peaks can be present:

Diagonal or autocorrelated peaks.

Off-diagonal or cross-peaks revealing direct J-coupling connectivity.

Relayed Off-diagonal or cross-peaks revealing relayed connectivity. A preliminary COSY spectrum can be helpful to differentiate from direct connectivities.

Axial peaks (appearing a F1=0) that are efficiently removed by using a two-step phase cycle.

Related experiments:

2D homonuclear experiments

2D gradient-based homonuclear experiments