Broadband homodecoupled NMR spectroscopy with enhanced sensitivity.

A new type of broadband homodecoupling technique is described, which is based on the original version of the Zangger-Sterk experiment, but results in a spectrum with higher sensitivity. The homodecoupling is performed by a combination of selective and non-selective 180° RF pulses in the presence of weak rectangular pulsed field gradients in a pseudo 2D experiment. The proposed experiment uses a fast pulsing approach to increase the signal-to-noise ratio per unit time. The recycle delay is significantly shortened typically to about 100 ms. After each scan, the offset of the selective shaped pulse is changed to access fresh magnetisation from adjacent frequency/spatial regions. The physical acquisition time was limited to 40 ms to keep the total length of the pulse sequence as short as possible. Broadband inversion BIP pulses are used instead of 180° hard pulses. They are used pairwise to cancel out unwanted phase shifts over the bandwidth. Reconstruction of the homodecoupled spectrum was done by concatenating the first 10 ms of the FID from each single increment to obtain the final homodecoupled proton FID followed by Fourier transformation. The new method can either be used to acquire broadband homodecoupled spectra in a shorter time or to increase the signal-to-noise ratio compared to the original Zangger-Sterk experiment. Using eight different frequencies can thus lead to a signal to noise gain of a factor √8 or a factor of eight in time.