The Single Pulsed-Field-Gradient Echo (SPFGE) scheme is a single echo experiment in which the central selective 180º pulse is flanked by two gradients. It is used for efficient selective and band-selective excitation purposes.
 

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

The SPFGE scheme consists of a single selective 180 pulse (S) flanked by two gradients G1 and G2 (G1-S-G2). When G1=G2 only the selected resonances will be refocused at the end of the echo whereas all other signals are efficiently dephased. An alternative scheme based in a double echo (DPFGE scheme) can remove some possible phase errors.

The phase properties of the SPFGE experiment are closely related to the phase properties of the refocusing element. Some advantages of the SPFGE and DPFGE schemes compared with other methods are:

Ultra-clean pure-absorption phase 1D spectra are simply obtained without frequency-dependent phase variations of the excited signal throughout the selected region.

No presence of sidelobes and/or sidebands outside the effective bandwith.

The full refocusing of all J-evolution at the end of the echo.

The sequence is very tolerant to miscalibrated pulses and rf inhomogeneities.

Requires no phase cycling, thus avoiding the need for difference spectroscopy.

Excellent results are always obtained with a very simple performance.

The SPFGE scheme has been succesfully incorporated in:

Selective excitation in 1D experiments:

Single selective proton excitation in selective ge-1D COSY  ( 95JMRA120-113 and 96JMRB124-110 ), RELAY ( 95JMRA120-113 and 96JMRB124-110 ), TOCSY ( 95MRC156 , 95JMRA257-113 and 95JMRB77-108 ),  NOESY experiment ( and 94JACS6037 ), ROESY ( 95MRC156 , 95JMRA257-113 , and 95JMRB77-108 ), and doubly-selective pseudo-3D as, for instance, TOCSY-ROESY and TOCSY-NOESY  ( 95JMRA124-113 ) experiments.

Single selective carbon excitation in selective ge-1D HSQC-NOESY ( 97MRC199 ) and GRECCO ( 95JACS9547 ).

Selective water excitation in water-selective ge-1D EXSY (PHOGSY) ( 95JMRA120-113 , 95JB306 , 96JMRB282-112 , and 95JB306 ) experiments.

Multisite selective excitation in selective ge-1D TOCSY experiment ( 96JMRB124-110 )

Selective excitation in 2D experiments:

Selective water excitation in water-selective ge-2D EXSY (PHOGSY) ( 5JMRB334-109 , 95JMRA120-113 , and 96JMRB282-112 ) experiments.

Band-selective excitation in 2D experiments:

Semi-selective proton excitation in band-selective ge-2D COSY ( 95MRC570 ),  TOCSY ( 95MRC570 , 96JMRB124-110 and 96MRC807 ), ROESY ( 95MRC570 and 96JMRB124-110 ), NOESY ( 95MRC570 and 96JMRB124-110 ) , DQ/TQ Experiment ( 96JMRB76-111 ), and 3D NOESY-TOCSY ( 96JB219 ) experiment.

Semi-selective carbon excitation in band-selective ge-2D HSQC ( 95MRC570 and 99JMR454-139 ), band-selective ge-2D HMBC ( 99JMR454-139 ) and band-selective ge-2D HSQC-TOCSY ( 95MRC570 ) experiments.

The SPFGE experiment can be run with minor changes from a predefined parameter set. The only parameter to consider is the selectivity of the selective inversion pulse: The user must define the shape, the duration and the power level needed for a defined excitation profile.

For further details on practical implementation on AVANCE spectrometers see Tutorial: SPFGE experiment.

The SPFGE scheme affords pure in-phase selective excitation without phase distortions in its whole excitation bandwith.

The SPFGE scheme can be included as a starting building block in any selective 1D experiment using the following basic general scheme:

Also see DPFGE scheme