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Selective 1H excitation
(using spfge)
PRELIMINARY SET-UP
  • Record a conventional 1H spectrum. Note the o1 of the selected resonance.
    • PARAMETER SET
    a selective excitation with rpar SELGPSE all (the pulse program selgpse

    By default, a selective 180º pulse of p12=20 ms with a gaussian shape (truncated to 5%) (gpnam1=gauss5) is defined. If other shapes want to be used, the selective 180º pulse must be recalibrated.

    MODIFY SPECIFIC PARAMETERS
    o1 is set on-resonance of the selected resonance.

    Clean excitation profile must be obtained in a single scan. If selectivity needs improvement, a longer selective 180º pulse must be chosen. See the following table as a reference:
     
     

    Pulse duration
    (p12)
    10 ms
    20 ms
    40 ms
    80 ms
    Bandwith
    (in Hz)
    140
    70
    40
    25
    Expected power 
    level (sp1)
    55
    61
    67
    73
     

    In such cases, repeat the acquisition process after change the p12 and sp1 values accordingly to required selectivity. These conditions can be applied without modifications in any selective 1D experiment using the SPFGE scheme as a starting point. See several experimental excitation profiles of the SPFGE scheme.

    ACQUISITION
    PROCESSING
    PLOT
    OBSERVATIONS
    The best option is to use the shorter selective 180º pulse that achieve clean excitation of the selected resonance without disturb other resonances. In some cases, the use of long selective pulses can undergo sensitivity losses due to relaxation effects.

    This experiment can be also performed using the non-gradient version of the selective echo experiment. The only difference is the need for a minimum two-step phase cycling.

    This same experiment can be used for band-selective excitation. In such case, the use of a more suitable pulse shape can improves the excitation profile of the sequence (for instance, a REBURP pulse gives excellent results).

    OTHER RELATED VERSIONS
    An alternative method for selective excitation is the DPFGE scheme which uses two selective echoes under the same experimental conditions as described for the SPFGE scheme.

    The SPFGE scheme can be succesfully used as a starting point to many selective ge-1D experiments as, for instance:

    Selective ge-1D COSY
    Selective ge-1D RELAY
    Selective ge-1D TOCSY
    Selective ge-1D NOESY
    Selective ge-1D ROESY