The R2D3 approach to fast quantitative NMR: maintaining accuracy and reducing experimental time

Abstract

Quantitative NMR experiments, especially on low-abundance nuclei such as 13C, can be extremely time-consuming due to the various constraints to ensure the quality of the results: high number of scans and long recovery delay. We propose the combination of the DEFT pulse sequence and the R2D2 method, hereafter referred to as R2D3. The addition of the DEFT to the R2D2 method reduces the quantitative limitations imposed by partial saturation. The parameters influencing the accuracy were evaluated with simulations and the quantitative performance of R2D3 were assessed by observing the trueness and precision on three different samples. The effect of different processing - the number of added rows and apodization - are also discussed. A precision of 1% or less was obtained in almost all the cases, showing that the R2D3 approach can drastically decrease the experimental time, while retaining the key aspects of a quantitative experiment. A high time gain factor can be achieved, close to that of INEPT and without its drawbacks, when trueness is less critical than precision. The R2D3 method will particularly benefit qNMR applications based on observing heteronuclei and analysing large sample series.