Time Domain (TD) NMR Proton (1H) Mobility Sensor to Assess Oil Quality and Oxidation

Abstract

The induction phase is the first step of oxidation, after which initiation phase occurs and is characterized by 1H abstraction and increasing peroxide levels. Later, the propagation cascade phase is generated with significant chemical and structural modification of the oil's fatty acids, causing increased concentrations of aldehydes. The process is terminated by the formation of toxic polymerization end products. A rapid and efficient analytical method of the different steps of oil oxidation are herein describe. Using a TD 1H NMR sensor capable of measuring proton mobility, it is possible to follow the segmental motion of the 1H population in each of the oil's segments, as well as describing the proton relaxation signals generated from the magnetic field that can measure and characterize important chemical and physical properties of the tested sample. In our research group's recent work, we demonstrated the ability to quantitatively measure the rates of self-diffusion (D) as well as ILT T1 and T2 spectral fingerprints of heated oils to correlate these values with chemical and morphological changes during oxidation. To simplify and reduce the time required for characterizing oil quality and oxidation using a TD 1H NMR sensor the present study focused on the relationship between D and the thermal and air conditions for enhancing oil oxidation. An excellent (R2>0.95) correlation of D with oil oxidation's conventional colorimeter standard tests (e.g., PV, p-Anisidine and TOTOX) was shown. These results were obtained from a high temperature (80°C) oxidation study of a list of saturated, monounsaturated and polyunsaturated edible oils (linseed, soy, olive, coconut, butter, respectively). The study clearly showed that self-diffusion D values, reflecting the mobility of 1H protons, is an accurate and rapid (< 1 minute) marker/indicator for the oil's quality with emphasis on the oils oxidation status, that be measured and used in the oil industry.