The INEPT block has been widely used to design multidimensional NMR methodologies. It permits to obtain sensitivity improvements by polarization transfer from the high-sensitive ¹H nuclei to low-sensitive X nuclei as ¹³C and ¹⁵N. In addition, it usually permits to use a faster pulse sequence repetition. Some enhancement factors for NOE and INEPT schemes with X{¹H} pairs of nuclei:

 

X	11B	13C	15N	29Si	57Fe	103Rh	109Ag	119Sn	183W
NOE	2.56	2.99	-3.94	-1.52	16.48	-16.89	-9.75	-0.41	13.02
INEPT	3.12	3.98	9.87	5.03	30.95	31.77	21.50	2.81	24.04

 
The INEPT block consists of the following steps:  
• A 90º ¹H pulse to create transverse magnetization (I_y).
• An heteronuclear spin-echo fixed period to allow evolution of heteronuclear coupling constants. Simultaneous 180º ¹H and X pulses should be applied at the middle of this period to refocus chemical shift evolution. At the end of this period, antiphase ¹H magnetization with respect to X is obtained (I_xS_z).
• Simultaneous 90º ¹H and X pulses transfer polarization from ¹H to X. At the end of the INEPT sequence, antiphase X magnetization with respect to ¹H is obtained (I_zS_y).
This antiphase X magnetization can further evolve to achieve in-phase X magnetization with respect to ¹J_CH (using the refocused INEPT or the DEPT block) or to achieve anti-phase X magnetization with respect to a third nucleus.

Easy implementation on AVANCE spectrometers.

The evolution delay must be optimized to 1/2*¹J_XH. For further details about implementation of 1D INEPT and 1D DEPT experiments in AVANCE spectrometers see, for instance:

• Tutorial: 1D INEPT experiment
• Tutorial: 1D DEPT experiment.

The standard way to implement the basic INEPT block in a pulse program should be:

... (p3 ph1):f2 d4 (p4 ph2):f2 (p2 ph4) d4 (p3 ph3):f2 (p1 ph5) ...

in which:

p1 and p2 are the 90º and 180º X pulse (in microseconds) applied at a power level pl1 from the f1 channel

p3 and p4 are the 90º and 180º ¹H pulse (in microseconds) applied at a power level pl2 from the f2 channel

d4 must be optimized to 1/4*¹J_XH

All phases are specified at the end of pulse program.

Analog blocks using several different commands can be used in inverse detected experiments in which the ¹H and X channels are exchanged. Thus, for ¹H-¹³C inverse detected experiments we have (see hsqcph):

... (p1 ph1) d4 (p2 ph2) (p4 ph4):f2 d4 (p1 ph3) (p3 ph5):f2 ...

and for ¹H-¹⁵N inverse-detected using the f3 channel we have:

... (p1 ph1) d26 (p2 ph2) (p22 ph4):f3 d26 (p1 ph3) (p21 ph5):f3 ...

The INEPT block is used as a preparation period of many NMR experiments as, for instance, the 2D HSQC experiment which is the basis of many 3D and 4D triple-resonance experiments specifically designed for labeled biomolecules. See some examples: