1H DOSY
Following the suggestion of Socha , analytical limitations of 1D1H NMR applied to plant oils were circumvented using diffusion-ordered NMR spectroscopy (DOSY) ). DOSY is a widely used pulsed field gradient NMR technique that separates species according to their diffusion coefficient (D) .
Oil undergoes hydrolysis, oxidation, and polymerization during heat treatment, resulting in the formation of compounds that have a higher molecular weight and higher polarity than normal unaltered triacylglycerols. Higher molecular-weight compounds diffuse more slowly than those of lower molecular weight and therefore DOSY can easily differentiate them.
In the origin method to measure D, of Stejskal and Tanner in 1965, a Hahn spin echo sequence is used with insertion of two linear magnetic field gradient pulses (G), of δ duration and separated by delay Δ, during the echo periods (Figure S1 ). At the beginning of the experiment the net magnetization is oriented along the z axis and the 90° pulse rotates the magnetization in the reading plane x-y. At time t, a pulse gradient of δ duration and G magnitude is applied (in the z direction) to encode the position of nuclei in the sample. After t again, a 180° pulse and another pulse gradient of the same duration and magnitude of the previous are applied to decode positions of nuclei. Without diffusion the echo signal is maximum. Movement of magnetic hydrogen nuclei causes echo attenuation. Faster diffusion (molecular translation) causes greater attenuation of the echo signal collected.