Determination of Carbon Chain Lengths of Fatty Acid Mixtures by Time Domain NMR

Average carbon chain length is a key parameter that defines the quality of liquid biofuels. In this paper, a method for the determination of carbon chain lengths of fatty acid mixtures is presented. The approach is based on proton relaxation rates measured by time domain nuclear magnetic resonance. The spin-spin relaxation rates R2 were used for the estimation of the carbon chain lengths. The method was examined for the set of samples with different mean lengths of the main linear carbon chain. Samples were prepared using four different fatty acids and mixtures of two, three or four of these fatty acids. The correlation coefficient between the known and measured values was equal to 0.994. Based on the relaxation theory, a linear-like dependence between the relaxation rate and carbon chain length was briefly shown, which endorses the experimental results. The developed methodology for determining carbon chain lengths offers robustness and rapidity, which are significant advantages when it comes to online use of the method in real industrial environments.