Figure 1. A high-resolution 2D PELF sequence with proton spin mixing.

During the t₁ period, the dipolar coupling between H1 and X (in this case, a carbon) nuclei is encoded under proton-proton homonuclear dipolar decoupling, then a 90° pulse converts the transverse proton-magnetization to the z-magnetization. On the ¹H channel, 180° pulse is applied to refocus proton chemical shift and a simultaneous 180° pulse on the X channel is applied to prevent the refocusing of ¹H-X dipolar coupling during the incrementable t₁ period. After a mixing period (t_mix) to allow proton spin diffusion, the ¹H z-magnetization is transferred to X-spin z-magnetization using the WIM (Windowless Isotropic Mixing sequence; it consists of 12 90° pulses without any delays between them with RF phases: −x, y, −x, −x, y, −x, x, y, x, x, y, x) sequence. A 90° read pulse is applied to acquire the transverse magnetization of X nuclei. The ‘homospoil’ pulse is applied before the preparation of proton magnetization for each scan to completely suppress any X spin magnetization after the completion of the signal acquisition. This is a 2D PELF sequence when t_mix is set to zero. (B) A model spin system considered for simulating the efficiency of the pulse sequence given in (A); the simulated results are given in Figure 3.