Constant time

Collecting multi-dimensional spectra requires recording chemical shift information via the use of an incremented delay. Since the length of the delay increases over the course of the experiment the signal is recorded at different times for each increment. This allows coupling in the indirect dimension to evolve, which broadens the peaks and decreases resolution. The "constant time" method was developed to eliminate this problem.

Two-dimensional NMR

The development of two dimensional NMR in the 1970s was probably the greatest advance in the history of the technique. The addition of another dimension to NMR spectra expanded the types of information obtainable and made possible the vast array of tailored multi-dimensional experiments available today. The development of two dimensional experiments relied upon the introduction of pulsed NMR and the use of the fourier transform to process the data. To generate two dimensional data a variable delay between two pulses must be used. Incrementing the variable delay allows chemical shift information to be regularly sampled and later processed with the fourier transform to give a second dimension. Read on for more details.