The selective ge-1D TOCSY experiment permits to obtain high-quality 1D TOCSY spectra from which J-coupled spin subsytems can be easily recognized. It is the gradient-enhanced version of the selective 1D TOCSY experiment.

Easy implementation on AVANCE spectrometers equipped with pulsed field gradients and selective excitation using shaped pulses.

The selective ge-1D TOCSY experiment consists of three parts:

Selective excitation of the selected resonance using the SPFGE block or the DPFGE block.

Mixing period to achieve in-phase polarization transfer to other spins. This is usually achieved applying some isotropic mixing sequence like MLEV, WALTZ or DIPSI pulse trains. This in-phase transfer avoids possible cancellation when the coupling is poorly resolved (see TOCSY Block).

Proton detection as usual.

Gradients can be incorporated in this basic scheme in two different ways depending if a refocusing gradient is inserted before acquisition. If is is not incorporated, EXORCYCLE must be applied on a selective 180º pulse of the SPFGE or DPFGE scheme. If it is incorporated, ultra clean 1D spectra are obtained without need of phase cycling but half of the signal is lost with compared to a non-refocused experiment (selection of N- or P-type data as a function of the intensity of this refocusing gradient).

The first published version of the selective ge-1D TOCSY experiment used the SPFGE scheme and the refocusing gradient ( 95MRC156 , 95JMRA257-113 , and 95JMRB77-108 ). Improved versions uses the SPFGE ( 95JMRA120-113 , 96JMRB124-110 ) and DPFGE ( 96JMRB183-111 ) schemes as a initial selective excitation block without the refocusing gradient ( 96JMRB183-111 and 97JMR267-124 ). Clean spectra with full sensitivity are obtained using a minimum two-step phase cycle. Gradient can also be incorporated flanking the DIPSI scheme in z-filtered TOCSY experiments ( 97JMR248-126 ).

Multiple-site TOCSY experiment using shifted-laminar pulses has been described ( 96JMRB124 and 98JMR162-130 ). The selective ge-1D TOCSY experiment can also be used as a starting point in other selective 2D experiments as for instance, 2D selective-TOCSY-COSY experiment ( 98JMR173-133 ) and 2D selective-TOCSY-TOCSY experiment ( 98JMR162-130 ).

The selective ge-1D TOCSY experiment can be run with minor changes from a predefined parameter set. The best option is the version which uses a SPFGE or DPFGE scheme as a selective excitation and the refocusing gradient is omitted. Two important parameters to consider are:

Selectivity of the selective inversion pulse: the user must define the shape, the duration and the power level needed for a defined excitation profile.

Optimization of the mixing period (as a function of 1/(J(HH)). When long mixing times are employed, magnetization is transferred to the whole spin subsystem, similar to the multiple-step RELAY experiment.

 For further details on practical implementation on AVANCE spectrometers see Tutorial: selective ge-1D TOCSY experiment .

In 1D TOCSY spectra, only protons belonging to the same spin subsytem appear as in-phase multiplets. The use of gradients allows to obtain a clean, artefact-free spectrum in a short time from which careful analysis of the multiplets can be done.

 Selective ge-1D RELAY experiment