The ge-2D semi-selective TOCSY experiment is a gradient-enhanced band-selective version of the 2D TOCSY experiment. By the use of some band-selective excitation method, only part of the 1H spectrum is evolving during the conventional variable t1 period or/and the proton acquisition period. In this way, a conventional 2D TOCSY spectrum is partially recorded with improved resolution and t1-noise.

Easy implementation on any AVANCE spectrometer equipped with pulsed field gradients (PFGs) and selective excitation using shaped pulses.

The most simple way to convert the classical 2D TOCSY pulse sequence to a gradient-based F1-semi-selective 2D TOCSY pulse sequence is replacing the initial 90º 1H pulse by a SPFGE ( 95MRC570 , 96MRC807 , and 96JMRB124-110 ) or DPFGE ( 96JMRB46-113 , 97MRC9 , 96MRC807 , and 98JMR154-132 ) scheme. The SPFGE block is prefered because minimizes sensitivity losses due short transverse relaxation times without to sacrify selectivity.

It is also possible to incorporate an SPFGE scheme as a refocusing pulse at the middle of the evolution variable period  ( 96JMRB46-113 , 96MRC807 , and 97MRC9 ) in order to remove unwanted couplings in the F1 dimension and, therefore, achieving improved resolution in this dimension.

Band-selective excitation of the F2 dimension can be equally performed by incorporating another SPFGE block after the TOCSY mixing time. Both band-selective excitation schemes can be combined in a same experiment. In modern spectrometers equipped with digital filters, automatic selection on the F2 dimension could be accomplished without the need to include the second SPFGE block. It is important to choose a shaped selective pulse giving excelent selective inversion profile as, for instance, a RE-BURP sequence.

Tutorials: 2D homonuclear experiments

Tutorials: 2D gradient-based homonuclear experiments

Tutorials: 2D gradient-based homonuclear experiments in H₂O

The experiment is acquired an processed using the same experimental conditions as described for its phase cycle counterpart. The only difference is the presence of gradients. Thus, the user needs to define the strength, duration, shape of the gradients and the recovery delay. If PFGs are not used for coherence selection, clean phase-sensitive spectra can be obtained using a eigth-step phase cycle without sensitivity losses. The inversion profile of the selected SPFGE scheme migth be checked on the same sample.

Data is  analyzed as in a conventional 2D TOCSY experiment.

Related experiments:

2D homonuclear experiments

2D gradient-based homonuclear experiments