A band-selective composite gradient: Application to DQF-COSY

We describe a unique band-selective method that utilizes a selective composite gradient to simultaneously achieve band selection and coherence pathway selection. This element is similar to the composite gradient known as the CLUB sandwich except the original broadband pulses have been replaced with selective pulses and the strengths of the antipolar gradients have been unbalanced. In this way, only the signals within the inversion band will continue to dephase throughout the duration of the element and satisfy the proper encoding-to-decoding gradient ratio necessary for coherence selection. Apart from the inverted polarity and asymmetry of the gradients, the band-selective CLUB sandwich is identical to the DPFGSE sequence and provides many of its desirable characteristics. We have successfully incorporated the band-selective CLUB into the DQF-COSY pulse sequence to create a band-selective experiment that offers the selectivity desired for resolution enhancement while maintaining excellent phase behavior. This is demonstrated on the congested aliphatic region of the ionophorous antibiotic Lasalocid A.