The doubly-selective ge-1D ROESY-TOCSY (ROTO) experiment permit to obtain high-quality artefact-free 1D TOCSY spectra on a specific proton resonating in an overlapped region where typical on-resonance selective excitation is not feasible.

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

The basic scheme of the selective ge-1D ROESY-TOCSY experiment consists basically of two concatenated selective ge-1D ROESY experiment followed by a selective ge-1D TOCSY experiment. The following steps must be considered:

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

Mixing period that in its basic form consists of a low-power continuous-wave irradiation block for in-phase polarization transfer to other spins via NOE in the transverse plane (see ROESY Block).

Selective excitation of the intermediate NOE 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 (see TOCSY Block).

Proton detection as usual.

In the original work ( 97JMR267-124 ) gradients are incorporated to suppress unwanted magnetization and, therefore, there is no sensitivity losses due to coherence selection. Excellent spectral quality is obtained using a four-step phase cycle.

The selective ge-1D ROESY-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. Important parameters to consider are:

Selectivity of the first 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 time in the ROESY block.

Selectivity of the second 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 time in the TOCSY block (as a function of 1/(J(HH)). When long mixing times are employed, magnetization is transferred to the whole spin subsystem.

The final spectrum of a doubly-selective ge-1D ROESY-TOCSY experiment is a clean TOCSY spectrum of a specific relayed resonance appearing in a overlapped region of a 1H spectrum. It is needed that this relayed proton has NOE effect from an another well-isolated proton on which a previous selective 1D ROESY experiment could be applied.