INEPT and Related Pulse Sequences

We discussed INEPT in Section 9.5, where we used the vector picture to follow the time dependence of magnetization and grafted on quantum considerations to understand population changes and polarization transfer. With the density matrix, all parts of the process occur in a straightforward manner. It is useful to go through the calculation in some detail, as a number of important points can be illustrated. Moreover, we will examine some modifications of the pulse sequence that provide insight into polarization transfer and multiple quantum methods used in 2D NMR. 

---

Let s now look at the density matrix as it evolves for the pulse sequences that we outlined in Section 11.5. We have illustrated INEPT and related pulse sequences by the two-spin system in which I = H and S = 13C.The equilibrium density matrix can be considered as the sum of two matrices ... 

DEPT is usually performed with broadband H decoupling. It is relatively insensitive to the precise matching of delays with coupling constants, and so is much easier to use than the closely related INEPT or the JMOD (APT) (see section 3.3.2.3) sequence. DEPT, on the other hand, is more sensitive to pulse imperfections than INEPT or JMOD. 

The width of the final1H pulse in the DEPT sequence ( ) affects the intensity and phase (positive or negative) of the 13C peaks in a way very similar to the length of the refocusing delay A in refocused INEPT, according to the relation = nJA. The intensities are shown below for the three types of carbon in DEPT ... 

---