An investigation of the effect of pulse angle and interpulse delay time on the sensitivity of the fourier transformed 13C NMR spectrum of α-santonin

A two factor, four level factorial design over a large region of factor space indicates that a second order polynomial can be used to describe the relationship of pulse angle and delay time on the time normalized sensitivity of each of the 13C resonances of [alpha]-santonin. The response surfaces generated from these models are all hyperbolic. For the slower relaxing nuclei the maximum response is in the region of small pulse angles (~35°) and short delay times. A local optimum also exists in the region of intermediate pulse angles and long delay times . For the faster relaxing nuclei the maximum response is in the region of intermediate pulse angles (~55°) and short delay times. As expected, the faster relaxing nuclei show greater sensitivity than do the slower relaxing nuclei. In addition, the region of maximum response is broader for the faster relaxing nuclei. The intensity of the free induction decay and several combinations of individual peak heights are evaluated as possible assessing functions to determine the overall spectral quality. To be effective, an assessing function must be chosen or designed to determine accurately the worth of the response to the experimenter. As is typical in a multiple response system, there exists no one "best" or universal assessing function. The utility, merits, and drawbacks of these assessing functions are discussed.