The use of ATR‐FTIR spectroscopy to measure changes in the oxirane content and iodine value of vegetable oils during epoxidation

Abstract

A rapid attenuated total reflectance Fourier transform infrared (ATR‐FTIR) method was developed to simultaneously measure for vegetable oils both their oxirane oxygen content (OOC) and the change in their iodine values (IV) that occur during their epoxidation. The method uses the peak area of the epoxy functional group absorption (1497.3–1432.0 cm−1) to measure OOC and the HCabsorption associated with a carbon–carbon double bond (3017.5–3004.2 cm−1) to determine the relative changes in iodine value (ΔIV). Calibrations were developed by gravimetrically blending epoxidized canola oil (ECO) with unreacted canola oil (CO) to vary both OOC and IV. Oils including canola, camelina, and flaxseed were epoxidized, during which the OOC and ΔIV were tracked as a function of time using both the new ATR‐FTIR procedures and the standard ASTM methods. Both the OOC and ΔIV values measured by the ATR‐FTIR method correlate well to values from standard methods (R2 ≥ 0.992 and mean relative error of <3%). The FTIR procedure is simple and fast to perform and facilitates the determination of selectivity (conversion of double bonds into oxirane group) and the end‐point for the epoxidation reaction, which requires measurement of both OOC and IV.Practical applications: The ATR‐FTIR method described provides a simple, rapid, and accurate means for the measurement of OOC as well as changes in iodine value during the epoxidation of vegetable oils. This allows for the determination of the degree of conversion of lipid unsaturation into epoxides. This method can be employed by manufacturers and research laboratories to study, control, and optimize epoxidation processes.The ATR‐FTIR methods described in this paper provide a simple and rapid means of monitoring OOC and IV changes during the epoxidation of vegetable oils. These methods are calibrated against standard titrimetric procedures and have been shown to produce similar results. It is especially useful that OOC and ΔIV, the two measures that are most relevant for monitoring the progress of a triacylglycerol oil epoxidation reaction, can be obtained from a single analysis. This facilitates monitoring and optimizing epoxidation processes. If the initial IV of oil is known, the method can also be used to calculate the yield, conversion, and selectivity of the reaction, as well as a study the reaction kinetics.