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

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: a high number of scans and a long recovery delay. We propose the combination of the DEFT pulse sequence and the R²D² method, hereafter referred to as R²D³. The addition of 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 was assessed by observing the trueness and precision for three different samples. The effects of different processing steps - 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 the observation of heteronuclei and the analysis of a large sample series.