Advancing quantitative NMR for high-precision isotopic analysis with rnmrfit 2.0

Quantitative NMR is widely utilized in isotopic ratio measurement for determining the origins and authenticity of chemical compounds. Achieving high precision required for such analyses depends on accurately separating signal from noise, which is essential for reliable quantification of resonance peak areas. In this study, we present rnmrfit 2.0, an NMR peak-fitting tool tailored for high precision isotopic analysis. This new version incorporates semi-global peak fitting with automated peak region selection, achieving greater robustness and computational efficiency than previously reported. The newly developed software was used to explore the impact of two common spectral processing techniques, line broadening and zero filling, as well as the choice of baseline span on peak fitting precision. All three were found to have a significant impact on fit precision, with optimal settings for line broadening and zero filling deviating from what is commonly recommended for 13C spectra, at 1-3 Hz and 0.5-1.0, respectively. Compared to commercial tools including TopSpin and MestReNova, rnmrfit demonstrated superior precision and trueness, achieving precision as low as 0.26% for 2H and 0.16% for 13C. The new version of rnmrfit is available as an open-source executable, offering a scalable solution for isotopic analysis with minimal user input, paving the way for more reliable isotopic quantification.