Optimization of two-dimensional NMR by matched accumulation

An analysis of NMR sensitivity enhancements obtained using non-uniform weighted sampling, and the application to protein NMR

“…Given that this process of apodization also increases the SNR, it is important to compare the sensitivity of NUWS experiments on a like-for-like basis with apodized uniformly sampled data. Here we show theoretically and experimentally that, when this is done, the 'real world' increase in SNR is on the order 10-20% rather than 200-300% as previously suggested [15,16]. Nevertheless, we prove that the change in SNR is always favourable, and even these modest improvements may yet be useful for the study of challenging, sensitivity-limited samples.…”

“…A like-for-like comparison of NUWS spectra with apodized uniformly sampled spectra is essential to avoid unrealistic expectations of 2-3 fold increases in SNR [15,16]. When this is done, as shown here, SNR improvements are more modest, of the order 10-20% (Table 1).…”

“…NMR data were acquired on a Bruker Avance III spectrometer equipped with a TXI cryogenic probe operating at 16.4 T (700 MHz). 1 H, 15 N SOFAST-HMQC spectra were recorded in triplicate using both uniform sampling, and cosine and cosine-squared NUWS. The NUWS pulse program, and simple scripts for generating sampling schedules, are available from the authors on request.…”

“…Previous works examining the sensitivity of NUWS acquisition have reported 2-3 fold increases in the SNR per unit experiment time, due to the concentration of spectrometer time on early increments with the highest signal [15,16]. The approach may also be useful for sensitivity-limited solid-state NMR experiments [17].…”

“…In addition, this may improve the ultimate signal-to-noise ratio (SNR) of the experiment, making NUS methods attractive not just to samplinglimited experiments, but also to sensitivity-limited measurements. An extreme case of this strategy, in the limit of large numbers of scans, is non-uniform weighted sampling (NUWS) [15,16]. Here, all points on the Nyquist grid are sampled, but with a variable number of scans proportional to the sampling density function (Fig.…”