Alternative method to quantify biodiesel and vegetable oil in diesel-biodiesel blends through 1H NMR spectroscopy.

An alternative method is proposed for the quantitative analysis of biodiesel in diesel-biodiesel blends. It is based on hydrogen nuclear magnetic resonance (1H NMR) spectroscopy and applies univariate calibration, in which the integrals of the spectra are considered. Statistical comparisons between the results obtained from the method proposed here and from the infrared (IR) spectrometry method, which is recommended by the European Standard EN 14078, show that the 1H NMR method offers equivalent results compared with standard ones. Furthermore, the proposed 1H NMR method recognizes the difference between biodiesel and vegetable oil, whereas the IR method cannot. Therefore, the 1H NMR method developed to quantify biodiesel in diesel-biodiesel blends is proposed here as a more practical and efficient alternative to the official method, because besides quantifying biodiesel in blends, it indicates adulteration with vegetable oil, either as the intentional and illegal addition of this raw material or because of a low degree of transesterification conversion during biodiesel synthesis.