Optimizing water suppression for quantitative NMR-based metabolomics: a tutorial review

In nuclear magnetic resonance (NMR)-based metabolomics, the water suppression scheme is one of the elements that most impact the overall quality of the spectrum. The choice of the solvent suppression scheme and of the associated parameters has therefore a high impact on the accuracy of the resulting spectra. As a consequence, potential users of H-1 NMR quantitative metabolomics would certainly benefit from a set of practical tools and recommendations to choose the experimental parameters leading-for a specific metabolomics question-to the most accurate and precise analysis of H-1 NMR spectra with solvent suppression. This tutorial review is structured into four parts which address the following questions: (1) why suppress the water signal? (2) what are the difficulties in suppressing the water signal? (3) which methods are available to suppress the water signal? (4) which criteria are pertinent to optimize and compare the different methods? These four parts are completed by an experimental section describing in details all the pulse sequences and parameters used in this paper. For each method, the performances greatly depend on the chosen parameters. For instance, the robustness of the NOESY-1D block is significantly modified when the mixing time is changed. Therefore, we propose simple protocols that can be exploited to evaluate and optimize the performances of a water suppression method.