Work

Using experimental design and 13C satellites to optimize the measurement of the absolute concentration of ethanol in wine by 1H NMR spectroscopy

Year: 2025

Type: article

Abstract: Proton ( 1 H) NMR spectroscopy is routinely used for targeted food analysis. In alcoholic beverages, ethanol content is a key quality parameter. While 1 H NMR's inherently quantitative nature makes it ideal for absolute quantification of ethanol, challenges arise in complex matrices like wine. High ethanol concentrations, orders of magnitude larger than other constituents and co-solvents, can hinder accuracy due to phenomena such as radiation damping and intermolecular interactions. The present work investigates factors influencing absolute ethanol quantification by 1 H NMR, including ethanol concentration (0–40 % v /v), solvent for signal lock (D 2 O vs. d-DMSO), pulse sequence (w/wo water suppression), NMR signal (main triplet vs. triplet's 13 C-satellite), quantification method (multivariate curve resolution vs. integration by raw sum), and sample type (red vs. white wine). FT-IR was employed as reference method for ethanol absolute quantification. Our results indicate that the highest accuracy for the absolute quantification of ethanol in ethanol-water solutions is achieved by measuring D₂O-containing ethanol solutions with water suppression, and raw sum for quantification of the ethanol main triplet and its satellites. . As for wine samples, wine type affected the quantification the most (ASCA effect size = 60 %, p < 0.001). Based on our results, the best approach to obtain accurate absolute quantification of ethanol in wines samples entails the use of (1) an external standard with its satellites ( i.e. , TSP), (2) a correction factor k ext , calculated from measurements of a known ethanol reference sample to compensate for misquantifications due to matrix effects, and (3) combining the intensities of the main triplet and its satellites for absolute quantification , in order to compensate for different 13 C/ 12 C ratios in wines. Using this method a correlation coefficient (R 2 ) of 0.99 and RMSE of 0.23 % ( v /v) was achieved for absolute quantification of ethanol in wine samples.

Source: Food Research International

DOI: 10.1016/j.foodres.2025.116598