Increasing the efficiency of multidimensional NMR experiments by varying the number scans in the indirect dimension

Sensitivity and resolution are perhaps the two important parameters that have concerned NMR researchers since the inception of NMR. The increase in magnetic field strength of new NMR spectrometers has led to improvement of these two parameters, but there are other ways to address these problems. The sensitivity of NMR is dependent on the number of scans while the resolution is dependent on the decay of the signal (i.e., the effective duration of the acquired signal). Thus, directly increasing the number of scans and the effective acquisition time can improve sensitivity and resolution, respectively. In experiments that require acquisition of series of FIDs with each increment of the series corresponding to an value of an incremented parameter (e.g., a delay), such as in multidimensional NMR experiments, each FID has conventionally been acquired with the same number of scans – but this need not be the case. We have shown in our previous study [1] that by varying the number of scans and proper scaling, the experimental time required for pulsed-gradient spin-echo (PGSE) diffusion and T1 inversion recovery experiments can be drastically shortened. A very recent study has successfully applied a similar technique referred to as apodization weighted sampling [2] to HSQC and HNCA experiments. In this study, we varied the number of scans for the series of FIDs that constitute COSY and q-space diffusion imaging data sets. The number of scans was manipulated to shorten the experimental time and/or achieve the desired sensitivity or resolution. This new approach is compared to the conventional acquisition scheme to illustrate its effectiveness and increased efficiency for acquiring multidimensional spectra