The HSQC experiment is a highly sensitive 2D-NMR experiment and was first described in a H—N system, but is also applicable to other nuclei such as H—C and H—P.  The basic scheme of this experiment involves the transfer of magnetization on the proton to the second nucleus, which may be N, C or P, via an INEPT (Insensitive nuclei enhanced by polarization transfer) step.  After a time delay (t), the magnetization is transferred back to the proton via a retro-INEPT step and the signal is then recorded. In HSQC, a series of experiments is recorded where the time delay t is incremented.  The H signal is detected in the directly measured dimension in each experiment, while the chemical shift of N or C is recorded in the indirect dimension which is formed from the series of experiments.