1. Purpose

The APT (Attached Proton Test) technique is a modification of the SEFT experiment and also differentiates between C, CH, CH₂ and CH₃ groups (see Exp. 6.3). The SEFT sequence suffers from the use of a 90° excitation pulse which requires long repetition times. In the APT experiment a shorter excitation pulse is used, but therefore an additional 180° pulse is required. Alternative methods that give information about the multiplicities are INEPT, DEPT, DEPTQ and PENDANT (see Exps. 6.5–6.12), and the old off-resonance ¹H-decoupling technique (see Exp. 4.11). Unlike INEPT or DEPT, the APT method yields ¹³C NMR spectra that are only enhanced by the NOE. However, APT also gives information about quaternary carbon atoms. Improved modifications of APT are known [2–4].

2. Literature

S. L. Patt, J. N. Shoolery, J. Magn. Reson. 1982, 46, 535–539.
J. C. Madsen, H. Bildsøe, H. J. Jakobsen, O. W. Sørensen, J. Magn. Reson. 1986, 67, 243–257.
A. M. Torres, T. T. Nakashima, R. E. D. McClung, J. Magn. Reson. Ser. A 1993, 101, 285–294.
U. Beckmann, W. Dietrich, R. Radeglia, J. Magn. Reson. 1999, 137, 132–137.

3. Pulse Scheme and Phase Cycle

APT carbon-13 double spin-echo sequence with proton composite-pulse decoupling